The reason IMO that Google is showing some pretty stupid serps is down to filters which I think have been applied to various targeted searches.
I've read a load of boards and Google have some serious bridges to mend with webmasters in general.
Rumours are that Google are attempting to boost their advertising revenue, ahead of their IPO.
The following will not prove that filters have been applied totally, but it is an interesting development.......
http://www.google.com/search?hl=en&l...=Google+Search
Notice that I've searched for xxx and told Google to ignore pages which contain a word I made up (nonsense word)
Now check out what Joe Surfer gets.....
http://www.google.com/search?hl=en&l...c2coff=1&q=xxx