This,
tbh. Why go to the effort of hacking TrueCrypt when a simple trojan or code execution attack will circumvent the need to hack it anyway? User idiocy is always going to be the number one cause of security breaches - encryption is much like a bike lock: there to persuade 99.9999% of potential criminals that it's simply not worth the effort. For the 1 in a million situation where someone really wants to get your data, they'll find a way (in much the same way as a professional bike theif who really wants to get your bike will find a way even if it's secured with a sold secure gold-rated lock - but I may be venting on a personal frustration now...
).
And, of course, an obligatory xkcd reference:
http://xkcd.com/538/