tedster - 7:37 pm on May 3, 2010 (gmt 0)
A number of other members have mentioned seeing this in recent days - and it may not have anything to do with a true problem on your site - especially because your home page comes up for a simple domain name query.
In fact, in a funny kind of way, this is sometimes a sign of something good - as long as it clears up. One of the things Google apparently does is maintain various lists of domain names for certain purposes. One of the main reasons is maintaining a list of domain names with a high trust or brand value.
When G is moving lots of data around on their back end, sometimes these dedicated lists don't get completely imported into the "final" big list and then the domain name goes missing from the site" operator results. This happened about a year and a half ago in a big way - and several very big name domains saw a temporarily missing home page.
While it is always good to have an eye on possible canonicalization problems [webmasterworld.com] (suratmedia's advice is excellent), you may well have nothing to fix.