Hello,
I am also having a similar issue only Minecraft crashes when it tries to create a new world. I used the latest version of Forge and did a clean install. I used an app called The Unarchiver to unpack Minecrafts .jar file. I then copied the new files from forge into the .jar file replacing the one's that were already in the file with forge's files and deleted the META-INF file. I started up Minecraft and clicked single player. I then tried to create a new world and it crashed. I have googled this issue and came here and only found this thread regarding this issue. The crash report is in the spoiler tag. I could not find the ForgeModloader log file. I do not have any mods installed, I am using the official client, and the latest universal build of Forge.
Edit: Found the Forgemodloader log I appear to have the same issue cpw pointed out after going through Forge's log. I can run the standard minecraft.jar just fine. I only encounter a problem when I try to use Forge
Minecraft Crash Report
Forgemodloader log:
