This is not a bug report but rather something to be aware of if you use the facebook API and URL Rewriting.
My environment I use iFinity URL Master and I recently installed a like button on my pages with ActiveSocial. In my case I had a site summary on my home page that was getting hit almost every second and thus generating an error log entry every second as well. The Log Viewer freaks out when the error log grows too large.
My logs indicated Page Load Exceptions originating in an ActiveSocial method and showed the absolute URL to be the page that had been appended with "?fb_xd_fragment"
This is part of what the facebook API does and there may be a bunch of other parameters as well. The URL is not seen by end users. I presume it does this call using AJAX behind the scenes.
You can easily test this scenario by adding "?fb_xd_fragment" to your user profile pages and check the log for errors.
Long story short, I tole UM to not rewrite if the URL contained "fb_xd_fragment" and it seems to be working in all respects. The end user sees nothing different and the API seems to work fine.