I believe Avast has walked the advertisement line pretty well. A colleague of mine actually took advantage of one of the Avast ads offering discount b/c he wanted the pro edition.

Also with Nevisos point about the Google/Avast partnership. I believe Google also bundles Avast in the google pack. The bigger the Avast free user base, the bigger the potential for new Pro Avast users which incidentally requires sporadic advertisement.

Also there shouldn’t be a problem with Avast getting a small cut for every new Chrome install with the pop up. It is relevant stuff, infrequent and it isn’t intrusive. If avast did what Avira did with the ask.com toolbar basically trojaning the thing in new installs or update prompts, then we will have a problem.