Not sure if anyone else has noticed this - for keywords I tend to keep an eye on google is returning far less, but far higher quality, results.
Sites which usually appear (including a couple formerly at #1 but with little to no content) are still in the index, but now way down in the SERPS.
Interestingly, the old geocities problem (second completely unrelated geocities domain getting an indented listing) has also gone again (google have been playing with this filter for a while - it goes on and off).
Seems to me the on-page factors knob has been turned up.
hmm. well I am not seeing the same on Yahoo, but this is much like what most of us went threw this past spring with Google.
I.E.: Site is in Google, index comes up in the serps for 2-3 keyword phrases, but the index is missing for single keyword searches when all indicators show it should be number one or two. (currently is on the other servers)