Here's a little bug I hadn't come across before. While updating and testing some TradeDoubler links on one of my sites they all suddenly stopped working and returned this error:

Bad Request
Your browser sent a request that this server could not understand.
Size of a request header field exceeds server limit.

This turns out to be an Apache server error. Strangely, the links worked in Firefox but not in IE7 (my main browser). I was a bit confused and assumed that there was some kind of problem with the TradeDoubler servers. When the link stills didn't work after several hours I tried clearing out the IE7 cookies and, hey presto, that did the trick and all the links came back to life. Thinking about it, I'd clicked on a lot of TradeDoubler links with IE7 that morning while I was testing them. I'm thinking that maybe TradeDoubler just keeps on adding and adding to the same cookie until it can take no more and gives up the ghost.