I'm seeing some very strange results in Google's site: search at the moment. Google appears to be displaying only a very small precentage of the pages on the site. About 3 out of 5 of my sites are affected, and I've noticed the same thing on other sites (not related to me). Seems to be a datacentre thing as on one datacentre I get 256 results, and on another 26,100 results (mostly forum). The usual number is 10,000 (including forum dross pages). EDIT: OK so serps are behaving strangely for me too. For my forum (not the one in the sig) looks like it might be a duplicate content issue with the view by post, thread, search etc. A lot of stuff has gone supplemental. Maybe I'll let it settle down and then have a look at adding nofollow on the duplicate pages. Something is brewing....
Saw that thread It's the regular site: search from the google homepage. I noticed the 51 million page thread at WMW has started dipping into the issue, and people here have been talking about a big increase in site: search results, but haven't seen anyone mention a big drop on some datacentres. It's not just site search - I've had pages dropping out of the serps and being replaced by supplemental results of other pages on the same site - for example a forum thread (from the main index) disappears and gets replaced by a single post from the supplemental index that appears only when the query is entered in quotes. Again this only happens on some datacentres. I feel something has happened already on google.com - for the last week I've have twice as many google.com referrrals as normal, but today is the first day I've seen funny things happening on google.co.uk.
Google has been doing these rolling updates for some time now... the old concept of a static index that gets updated at regular intervals is long gone.
I think I must have come across a funny datacentre this morning. For some reason it just didn't seem to have many pages from my site or some other sites I looked at. Thinking about it, old numbers were showing for some of my other sites. I guess the datacentre was just being updated with all these new pages that other people and me have reported in the site search.