A WebmasterWorld thread documents that, at least two, people have seen a different number of results on the first page of the Google results, when compared to the second page of results. For example, you search on any keyword phrase and you are presented with Results 11 - 20 of about XXXX for keyword phrase. If you click the next button, to go to page two of the results, you are presented with Results 11 - 30 of about XXXX for keyword phrase, instead of Results 11 - 20 of about XXXXX for keyword phrase.
WebmasterWorld administrator, tedster, has confirmed that he has seen this as well.
The question now is, is this a temporary glitch or an other one of Google's tests?
I personally have not noticed it myself.
Forum discussion at WebmasterWorld.