...or at least on Freenode.
Donation addresses are everywhere here on the forum, and I've found a way to implement them on IRC. NickServ on Freenode supports the adding of arbitrary metadata to registered nicknames. Just type:
/nickserv set property donations <address>
where <address> is your chosen BTC address. You can also replace 'donations' with any other string, if you want.
Then, if someone on IRC deserves a donation, type:
/nickserv info <theirnickname>
and look for a 'Metadata' field to see if they've set an address.