Well, it's just not Pidgin -- it's the new plugin for Pidgin called "Bot Sentry" -- Bot Sentry is a free SourceForge (OpenSource) product and is, without question, the best anti-spam countermeasure for instant messaging. Nothing else comes close. This program will require any user not on your contact list to answer a predefined "Anti-Spam Question" first, such as "How do you spell the number 5?" If the question is answered incorrectly, you are never bothered. Also, Bot Sentry works on all chat services connected to with Pidgin!
So, you'll see me active on Yahoo (chazantonelli), AIM (mc4bbs), ICQ (174278712), MSN (firstname.lastname@example.org) and Google Talk (mc4bbs) services once again alive and ready to chat -- but be forewarned, you need to know how to answer the question I've set up in order for your message to ever been seen by me. Of course, the webcam and other specific Yahoo features won't work -- but it's a great trade-off to get rid of the spim (IM Spam.)
Note: I especially like this, as stupid people that don't read directions also get blocked -- not just spim robots! (Your I.Q. must be this big to ride this ride! ;-)