An Italian spb user has ported an hack he did for SPB to a FP Plugin.
JNotify plugin notifies a predefined Jabber user whenever somebody comments your blog.
I didn’t have time to test (I don’t usually log into jabber, really), but I think it’ll do the job :)
Well, kudos to fabrixxm (and kudos to Carlo :))
You can find both the hack and the plugin here