I had a huge number of legit pages replaced by crap that either redirects right to the sponsor, auto-installs spyware/trojans, or leads to pop-up hell. The main offending site was registered this past October

whereas my site has been online and listed since around 1999...
As well, Google has listed dozens of pages from my site that haven't been online in years, and all new listings (since around October) have been dropped. I've been in contact with them numerous times and have been told to we're sorry, we understand, wait for the next update, blah blah blah.
Luckily for me, Yahoo is doing a much better job indexing my stuff now so this winter hasn't been a complete loss. As for Google itself, I'm not using it nearly as much as I used to for my personal searches. Too much crap.