I just went into my account and figured hey, why not validate. Clicked on the link and I went straight to zero weight! I clicked it again, and my weight came back... Not really a question... just a sigh of relief.
I've done that a few times already. Once it took about a dozen clicks on the validate link before it came back up. Don't know why this happens. My site was up with ads the whole time.
The API isn't perfect. At times it returns 0 pages for a site, which results in a weight of 0 (but still passes validation).