It's sporadically available (as I write this it's back down so they must have been testing), but if you use maps online you'll be interested in clicking on this web address later today:

http://virtualearth.msn.com/

It's not officially released yet, but people are already talking about it, linking to it, and posting their screenshots. Crazy how this word of mouth thing gets around so fast.

Update: Scoble points to Chandu Thota, who is on the MSN-VE team. He says:

"Virtual Earth was live between 4 PM (PT) Saturday and 10 AM (PT) Sunday as part of our final cheks against our production systems; so we are now back offline as planned and be officially (beta) live on Monday. Our initial release is only limited to USA and we will follow up with other regions soon after that."

One question I have had about the service - Is the VirtualEarth API open like it is with Google Maps?  Update: The answer is apparently yes and the Via Virtual Earth developers' web site is already up to get those itching to integrate started.

This will be fun to watch. I especially like Google Maps, and it's new overlay mapping (hybrid maps on top of the satellite imagery) is cool, so we'll see if MSN Virtual Earth grows to compete over time . Some of the cool features are there already - but it'll be a tough race, for sure.

Oh and by the way, did you happen to see that Google released Google Moon the other day to commemorate the first landing on the moon? Don't zoom in too close. Apparently this is part of the Google Copernicus Hosting Environment and Experiment in Search Engineering R&D project. More info here.

Hey Microsoft, you got a moon initiative?
Update from Robert in the comments: Yes, they do.