The release candidate download page accidentally appeared on Microsoft's TechNet today, providing us with all the details we needed to know. We now know the RC will be released somewhere in May, and that it will continue to function until June 1, 2010, when it will expire (the beta will expire August 1, 2009). The RC program will run at least through June 2009, and there will be no limit on the number of keys given out, so hopefully we won't have the same situation as during the beta, when the download servers buckled under the pressure.
There will be downloads in English, German, Japanese, French, and Spanish, both in 32bit as well as 64bit versions. The hardware requirements listed are still the same as those for the beta release.
It's not far-fetched to assume that this "leak" is a simple marketing ploy by Microsoft. The automotive industry does stuff like this all the time, with "leaks" originating from the companies themselves, in the hope of making a double slam: all over the news when you "leak", all over the news when you announce.