Mod's review: Buildcraft

Short version: superb mod. Get it here (also there are some videos, and the building recipes). The autor's nick is Spacetoad.

Now with the more elaborated version:

• Components:

This mod can be broken into three different parts: pipes, machines and markers.
Markers are just that: placeholders that are used to select an area. The area can be a line (using two markers), a surface (using three) or a block (using three). The markers must be aligned in the same line with another, and their range is about 63 blocks (you can test this by making a line, and feeding the filler with two stacks of anything for rapid counting). They have an extra functionality very interesting for unrelated reasons: by placing a redstone torch near a marker, the marker will emit a blue line (that can go through solid blocks and liquids) to the max range of the block, in the six possible directions. I've used this to make a grid so I didn't had to count blocks to place trees, but there are more possibilities.
Pipes are, again, just that: tubes. They go from a machine or chest to anywhere you want, and are best used with the included machines in the mod. You can see what items go through them, also. There are several types of pipes:
Wood: when receives redstone current it takes one item from the attached block (usually a chest, forge or automated crafting table) into the pipe system. Using a clock seems to not be necessary, but it also seems to bug after 10 minutes of use in SMP, so I'll stick to clock using. They are brown-colored.
Stone: the battle horse, they are just black-colored pipes.
Steel: this steel-colored pipe acts as blocking pipe, allowing all the stuff going through it to exit only in one direction (so you will use it when two or more pipes join into a main lane). You can change the exiting pipe by right-clicking on the steel pipe, which also reacts to redstone current.
Gold: this yellow pipe works like powered rails, but it doesn't break any block inside it.
Diamond: light blue, with up to six colors added to parts of it, it's a sorting pipe. After right clicking on this pipe, you will see a window quite similar to the one used by large chests, but with color rows. You place an example in a row, and all the blocks of that type will exit the diamod pipe through that exit (or, if there is an exit without any example, the blocks which don't match the other filters will go through there). I found the only non-wasteful filter here is making cobblestone go into one exit, dirt, sand, sandstone and gravel into another, and everything else in a third one when using a quarry.
Obsidian: this purple pipe will suck any item dropped in front of it. However, the item needs to be in the same block, but you can add redstone current to enlarge the range to one extra block. Very useful if you don't want to be in the collection spot of a farming machine.
Redstone: this pipe has been added by Eloraam (the author of the Integrated Redstone mod), and it's a pipe that emits redstone current anytime a block goes through it. It can be found in here.
Machines: The Automated Quarry, the Automated Miner, the Automated Crafting Table and the Filler are the four machines in the mod.
automated Quarry: It's a machine that makes a hole in the ground every time it takes a right click or a redstone tick (so a clock is needed to leave it in automatic). The mined items go out from its upper side, and using a pipe system is very advisable since the machine will make a big hole all the way to the bedrock (or a lava lake, which is good if you have a water source falling into the bottom when it comes to harvesting obsidian). You can use three markers to select an area and thus deciding the size of the quarry, or you can let it be its default size. The olny downsides to the machine is that you require 11 diamods and 8 gold bars (plus 20 iron bars, 20 cobblestone and 22 wood sticks), which can be difficult. However, the machine can be picked after it has finished and positioned somewhere else.
Automated Miner: anytime you right click or apply a redstone click, this machine will dig a block downwards, leaving a placeholder pipe you can't retrieve but can easily break by hand (easier than leaves, I think). Like the Quarry, you can retrieve the machine after it has reached the desired depth (or bedrock), expels the mined block by its upper side, and can put what mines directly into a chest by its side (much more practical than doing that with the Quarry, since there won't be more than one stack of each block in the game). Since I have Industrialcraft (with a much more interesting mining machine), I only use this one to make infinite cobblestone machines that automatically output 2 cobblestone blocks to large chests (by placing 3-4 large chests, I can be sure it will take 23+ hours of continous gameplay before the chests get full).
Filler: the king of the realm, this machine will fill any area delimited by the markers (line, surface, volume...), but won't substitute any present material. Remember, it fills, so if you want to make a big house or a castle's walls, you need to make several vertical/horizontal surfaces, or you will get a big cube you will have to manually empty. And a 60x60x60 cube is 216.000 blocks, or 3.375 stacks!!! Also, since its top speed seems to be 1 block/second, you would need 60 hours of continuous gameplay (two days and a half) just to fill that.
Automated Crafting Table: this one, while very interesting, is (in my opinion) the least useful part of the mod. You put a recipe inside it the same way you would be using a regular crafting table, then exit (the machine won't spit the contents), and everytime you feed the table with the components you put in the master recipe, the table will craft it after receiving a right-click or a redstone click. So you would usually make a chain of  1 chest/large chest per used input, one wooden pipe per chest to get the items out, several stone pipes to get the stuff to the crafting table (plus a single steel pipe to ensure the items won't go through the wrong pipe), another wood pipe exiting from the table, and a chest/large chest to store the finished product.
While awesome, I think this is not really a practical machine, because... What crafted thing in Minecraft you need in enourmous quantities? Torches, sure, and steel pickaxes (or diamond ones), but it's better to carry 32 wood logs and 64 charcoal, using 2 slots to make 4 stacks of torches, for example.
Also, there is a problem in the table: you need to be able to stack the items for the Automated Crafting Table to work its magic, so forget about anything that uses buckets, and remember there are 3 different logs of wood, so you can't put several stacks of each one in a single chest and then feed it to a single table, it will only make wood planks from a single stack (and leave the other logs in the floor near the table).

I personally give the mod an 8/10, and commend the effort of the modder by making the latest version a SMP one.
I also think it would be awesome to be able to feed the filler with some predefined building plan, made from a .schematic file (and that would tell you how many blocks it would need of each material, both in single blocks and stacks), and let the machine run the job, also using the markers to define the area of the .schematic file to be made.