I noticed a higher than average number of rejects and investigated my glorious reject log for my site to find that a bot running from yandex.com was being denied. Well I did a little research (and even found Brett posting about yandex.com though not specifically the associated bot). It looks legit as far as I can tell though someone mentioned that the IP's are in a block associated with some undesirables. The main point is that you may or may not want to update your black/white lists accordingly. I would not mind hearing about the associated undesirables here though.