got a pretty big hosts file from some site, and had been adding to it myself, now additional blocking done via Adblock. Between them it probably nukes 4/5th of ads I guess? I only go add things to adblock if they're annoying - too many or flashy etc, I'm happy to leave things like google ads.
btw, since updating to firefox 1.5 (and relevant extension updates), blocked ads now show the "Unable to connect" message where they would have been (previously just showed nothing), and also clicking on the Adblock tab on flash ads etc does nothing. Any ideas what's gone wrong?