Heard on the IRC that once Buildcraft 2 comes out we might need to restart... but it looks AWESOME! Engines are a good idea. Allow basic Buildcraft opperations with constant redstone and demand resources to run more powerfull engines for powerfull stuff.
I wonder if IC miners on extractor mode work with modded liquids...
Oh, and I hope oil is flammable/etc! Make the enterence to your base need slogging through an oil pool with a murderhole above for lava dumping. Enemy = Broiled, shallow-fried, and magmatized!
I've been thinking for a while about the utility of gas/smoke grenades in Minecraft. Seeing as it is a voxel game, effects should be easily able to hug walls...
I was thinking that 4 torches + a slimeball + 4 sugar could make a smoke bomb that is thrown like an egg and spawns a block of "5smoke" that spawns "4smoke" in air around it and degrades to "4smoke".
Continue this pattern and make higher value blocks randomly spread to lower value ones (3 next to 5 = 4 next to 4) (this will cause some switching back and forth with blocks only one level different) and make "1smoke" vanish over time like unsupported leaves.
The effect is that a bunch of blocks spread out from the impact point, following terrain, and then vannish once spread too thinly.
There could be standard torch+slimeball+sugar opaque smoke, unbreathable torch+slimeball+ink sac smoke, and damaging torch+slimeball+gunpowder+redstone smoke.
This oil stuff is making me think of even nastier stuff, but I don't think giving the average minecraft player fuel-air bombs is a good idea.
... maybe if they didn't cause terrain damage and wasted the bucket too... and required gunpowder. Just spreading, incindiary smoke...