The last few days, a couple of sites that I know which had for example hundreds of pages indexed in Google were only showing a few pages in Google, with the command site:url.com. Google was displaying a message saying that some results were omitted while there was no reason for them to do so. (pages having unique title tags, search engine friendly urls etc.)
The problem was reported in WebmasterWorld and also on many other forums.

As of today, these sites that  I know are showing the same number of indexed pages as they were before the issue. Matt Cutts hasn’t commented on this issue yet. “GoogleGuy” over at WMW apparently said that he knew where the error came from and that they were working on it, but we haven’t seen anything on Matt Cutt’s blog yet.

I’ll be interested to see if people are still facing this issue, so please be kind to leave a comment if you do.