From time to time I receive this error page from various Google services like Gmail. I don't think I have ever encountered it with Google search though. Perhaps their search service is just too precious to be allowed to be afflicted with errors. This type of error generally indicates server unavailability due to various reasons, namely excessive traffic.
Receiving Web server errors is not unusual. It happens to all Web servers occasionally, specially the busy ones. It just feels unusual getting this error from Google, a company with seemingly endless resources and money. Along the same lines, Blogger.com (Google's blogging service) was slow as molasses two nights ago. It was so sluggish, it took me a half hour just to make a post. Seems to be back to normal tonight.