Try replacing the PSA's with high paying clicks themed to your site. That way you won't mind the occasions that Google shows PSA's. I had that idea and developed PSA.Replace on the back of it. Worls great for me. Give it a try at psareplace.com
We've seen a nasty PSA outbreak on our network for the past 48 hours... pages that have been live for a while, serving productive Adsense ads are now showing nothing but PSA's. Hopefully this will end soon.