I saw a 50% drop in indexed URLs a few days ago on one of my sites, and just today an increase in 500 on inbound links for the same site. Rankings seem to be unaffected.
I don't know if the lower number of indexed URLs is part of the same change - I think it is more likely to be different for different websites. I'm also guessing that the Webmaster Tools reports are in the middle of some big changes and those cahges are not all worked out yet. So I'm not going to react in any way to what I see right now, unless I also see a change in ranking or traffic.
