One Quirrell point to JoshuaZ for getting both of the reasons, rather than stopping after just one like jimrandomh did.
(I'm going to stop PGP signing these things, because when I did that before, it was a pain working around Markdown, and it ended up having to be in code-format mode, monospaced and not line broken correctly, which was very intrusive. A signed list of all points issued to date will be provided on request, but I will only bother if a request is actually made.)
Something a number of LWers should probably be cautious of.
http://www.nature.com/news/2011/110822/full/476373a.html