Microsoft pubCenter, an ad publishing tool (think Google Adsense) from Microsoft Advertising, after existing as a private beta for a number of months, goes into public beta today, April 22.

Kevin McCabe, Senior Product Manager for pubCenter beta, will be at AdSpace, (a part of the AdTech conference in San Francisco) today to announce the public beta and to speak on the state of contextual advertising.

pubCenter is actively seeking publishers to join and test contextual ads on their sites, and you can sign up for the beta at http://advertising.microsoft.com/publisher.  You can get more information about the program on the pubCenter blog, also coming out of private beta today.

We’ve been using pubCenter for some time on LiveSide on a trial basis, and will continue to test it in the months to come:

While we can’t comment on reporting and performance, we are quite happy with pubCenter, and encourage you to give it a try on your sites.

UPDATE: Sorry forgot to mention that yes, the beta is still US only: "Note  This is a U.S. only program at this time. You must provide a U.S. tax ID and address. "