I am seeing reports at WebmasterWorld of a possible Microsoft update to Live Search.
Senior member, bwnbwn, said it looks like Microsoft is jumping back and forth between two indexes. He said:
It looks to me that there are 2 data centers the serps and they are rotating in and out. One data center is presenting much better serps the other may be a way microsoft is working on the bot and is throwing the spammy one.
Others are not happy with the update, complaining that there is too much search spam at the top.
Forum discussion at WebmasterWorld.