I have a bunker under my house for a nuclear fallout, don't judge me! It's made out of cobblestone blocks and is 5 blocks below the surface and... in Minecraft. Maybe I should go outside more...
@Lachlan but if he's playing FTB, IndustrialCraft lowers the blast resistance of water and obsidian so that nukes actually affect them. He'd have to use Reinforced Wall and Reinforced Glass.
Depends on the mod. Horses definitely ruin Minecraft, however the stuff they put in FTB really adds to the experience, and you still enjoy Vanilla. In fact I enjoy both experiences equally.
Optifine actually makes FTB run slower - it's designed for Vanilla Minecraft, whereas all the mods do all kinds of crazy things that make Optifine's optimizations unhelpful.