Variation on the 50/50 split if you're like me and:
a) have recently downloaded something that's plumming up your game and
b) can't be plummed to go through six and a half gigs of CC:
Sort your mods folder by date modified and chuck out your latest batch of CC (e.g. your last six folders, which is what I ended up doing). Then, add it slowly back in as per usual. It took me 20 minutes to find the CC that was stopping my game from launching instead of 2 hours doing that! (P.S. I think it was TS3 CC instead of TS4, since they're .package files and that's happened before).
