In what was probably the worst beta testing I ever witnessed, the following happended:
The site was using frames.
All bug reports we got had the same URL (namely the entry page of the frameset)!
None of the client's "highly qualified beta testers" (which were supposed to not only find bugs, but also suggest solutions) even realized that they were on a frames page and thus reported an error on a shop page but posted the "www.foo.com/news" URL.
We ended up sending all reports back as "REJECTED: no error reproducable on reported URL". *Duh*