I've been trying to sort why MC has been crashing for the last 3 days w/ my favorite mods after not having played in some months, then had it in 5 after finding the 'errortest.bat' link in SDK's post.
Turns out, IC2 hates my key config. Binding right mouse button to move forward makes the house fall down. This happens the instant I load a world, or the instant I change my key config to this after having loaded a world. If it's any explaination, I've never kicked the RMB/ZXC that I learned back in Doom for WASD.
FWIW, options.txt contains: key_key.forward:-99
Probably not high on your bug priority list, but it'd sure please me to have it fixed. Also, my first post in the forums, and many 
's for a great mod.
Code
Mods loaded: 13
ModLoader 1.2.3
mod_MinecraftForge 1.4.1.61
mod_ModLoaderMp 1.2.3v3
mod_BuildCraftCore 2.2.13
mod_BuildCraftBuilders 2.2.13
mod_BuildCraftEnergy 2.2.13
mod_BuildCraftFactory 2.2.13
mod_BuildCraftTransport 2.2.13
mod_CraftGuide 1.4.3 for Minecraft 1.2.3
mod_IC2 v1.81
mod_LightSensor 1.2.3
mod_Stackables 1.2.3
mod_QuickGuide 1.2.3
Minecraft has crashed!
----------------------
Minecraft has stopped running because it encountered a problem.
--- BEGIN ERROR REPORT e778c7c5 --------
Generated 3/24/12 11:39 AM
Minecraft: Minecraft 1.2.3
OS: Windows 7 (amd64) version 6.1
Java: 1.6.0_31, Sun Microsystems Inc.
VM: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
LWJGL: 2.4.2
OpenGL: GeForce 9800 GTX/9800 GTX+/PCIe/SSE2 version 3.3.0, NVIDIA Corporation
java.lang.IndexOutOfBoundsException
at java.nio.Buffer.checkIndex(Unknown Source)
at java.nio.DirectByteBuffer.get(Unknown Source)
at org.lwjgl.input.Keyboard.isKeyDown(Keyboard.java:399)
at ic2.platform.Keyboard.isForwardKeyDown(Keyboard.java:19)
at ic2.platform.Keyboard.sendKeyUpdate(Keyboard.java:42)
at ic2.platform.Ic2.onTickInGame(Ic2.java:343)
at ModLoader.onTick(ModLoader.java:1109)
at EntityRendererProxy.b(EntityRendererProxy.java:22)
at net.minecraft.client.Minecraft.x(Minecraft.java:892)
at net.minecraft.client.Minecraft.run(Minecraft.java:747)
at java.lang.Thread.run(Unknown Source)
--- END ERROR REPORT 178be5f ----------