Never go to sites that require you to register a username, even on TOR. The last great bust didn't get anyone necessarily because of exit nodes, afterall, the entrance nodes are still chains of servers behind the exit node, no my anon friends, what got them was posting things under a certain username on several boards. They either posted enough information to get them caught or someone they trusted shat on them. TOR is pretty safe but make sure you go into your about config file and turn off javascript. Oh and don't forget to get truecrypt, install TOR on your truecrypt partition, use a multipass erasing program, always rename your downloads, once finished using TOR, multi pass delete your dns cache, your firefox files, backup first your prefs.js and places.sqlite files, then restore them. While you do the deletion it's good to turn off your wireless card in case some trojan is broadcasting, then once back up, go into your router and change your ip address. Also a good idea to spoof your computer's MAC address. If you are simply cleaning out your cookies, you probably ought to do some research.