Andylew - 7:31 am on Jun 1, 2010 (gmt 0)
Then that's not the same as an algorithm change. The Mayday change was aimed at algorithmic ranking for long-tail results. Matt Cutts also emphasized that Mayday was an algorithm change and not an indexing change.
There have been ongoing reports here of losing pages in the index - and then some members reported seeing a gradual reappearance for some pages that were dropped. This sounds like a different process at Google, and a somewhat mysterious one at that.
The algorithm change could have needed a re-indexing of the long tail to factor in another variable? Matt would be telling the truth saying it is an algo change but not giving the complete story by saying a reindexing was required - that would be going beyond the question that was asked.
For us we still see only several thousand pages in the results compared to over a million being reported on WMT. Somewhere there is a blackhole of ~1 million pages.