I just noticed this. I've been working on one of my sites for the last few days. It has a specific niche and I have adsense on all of the pages. Anyway, I went to Digg today and noticed that their Adsense was feeding me ads from the same niche as my site even though the content on Digg is not related. Could it be that they're targetting users in addition to content? Eg, if I'm browsing a site with niche a, I may be interested in the same types of ads from niche a even though I'm currently browsing niche b.
Those ads seems to be related to PSP sites, so may be somewhere the keyword PSP could be there, can you please provide the exact url...
You can see there is lots of different topics with different keywords, so its pretty hard to predict that the ads are not relevant to the content, you should try with a page having few related keywords and I believe it will display only related ads on that page..