As of late my mains site has been dropping in backlinks, pretty rapidly. Any reasons for this? Apart from the obvious link partners stop linking back. I heard someone say before a pr update this happened. Any truth in that.
That can only mean that those links are being removed to my knowledge. If your link is on a website that doesnt have a NOFOLLOW it will count as a backlink and wont be removed. A possible scenario could be that pages that have your link on them are becoming de-indexed so that link will no longer count. Guess there is a few things that could be the cause but I can tell you it definetly has nothing to do with a PR update.
Its also hurting your ranking? If not then there is no need to worry ... I think iwebtool uses Google. You should use MSN {Live}, Yahoo! Site Explorer or Backlinkwatch {mine} for comprehensive backlinks report
it also happened to our site...try to use Submit Express or the great tool of Mong the Backlink Watch