I am up against a pretty restrictive and eager-to-make-a-point-of IT department who sees everything as black and white only. I believe the solutions here are superb and am pretty excited to have a bit of freedom again, but...
What is left behind as any kind of trace? I realize the MTU and Prefetch areas are populated on the PC...fine...I can delete those off. Anything else that I should be aware of? Even the slightest thing can make a difference...!
TDD.
If it means risking your job just so you can surf certain sites or check your personal email at work, I have 3 words for you:
DON'T DO IT.
Even without traces on the PC, you could get caught. They could install PC monitoring software without your knowledge. They could monitor your network traffic and see you're using an unapproved browser or IM client. Your boss could walk in on you.
PortableApps.com's platform leaves behind fewer traces than U3, Ceedo, etc... but that doesn't mean you can't still be caught.
Sometimes, the impossible can become possible, if you're awesome!
Most of the items off the USB card would be run when I am traveling, so that is not an issue...email, surfing, et. al. Network traffic would be via a hotel's network, or even my cellular aircard. Never at work...they have apparently nothing else better to do than keep eyes on me 8-)
TDD.