Personalized Search is raising a lot of concerns about privacy and quality of results, but I've still maintained that it'll be good for online advertising. The reason is simple: Behavioral Targeting Ads. As the PPC Marketing Guide explains:

Behavioral targeting ads are the practice of delivering ads to individuals based on their previous surfing behavior. Behavioral targeting advertising have been around for some time, however in the past year more advertising companies have been investing in expanding their networks and systems in order to increase their market share. Even Google has been moving towards behavioral targeting ads with their personalized search The idea behind behavioral targeted ads is to deliver users ads that their interested in. [...] Behavioral targeted ads create a more positive user experience and lower the the marketing costs for advertisers.

Behavioral targeted adswork by capturing what the user initially searched for and then serving text and/or rich media advertisements based on relevant affiliated websites that best match your user’s keywords or channels.

In a word, behaviorally targeted ads wouldn't be possible without personalized search, and that's why Google has been pushing the latter: because in the past year more advertising companies have been investing in expanding their networks and systems in order to increase their market share.

Of course, whether or not this adds up to a more positive user experience is up to debate. It does make for a more positive consumer experience, though. The thing is that websites are free to access, there's no such thing as a free lunch, and you have to pay one way or another. You pay by being exposed to advertising, and adservers are going to have to find a way to make sure that those ads are worth the advertisers' budget dollars. Otherwise, the show is over, and we'll all go back to paid subscriptions to read newspapers online.