Well, IE9 has seven Platform Previews (granted, those are only for developers and not the general public - which is why Microsoft didn't bother giving them the "full" UI - but still) out,
plus Beta #1 (which came between PP5 and PP6) and a yet to be released Beta #2. Opera also displayed a similar behavior with 10.X's large number of alphas and betas - not to discount the RCs (which would sometimes be re-tagged as RTMs because the Opera Team thought there was no need to compile a new build just so that it could proudly carry the word "final").
Speaking of Opera, 11.0 hasn't crashed on me yet, which is an
excellent performance in my book (hope I just didn't jinx myself here
) after all the nonsense 10.63 put me through...and I'm absolutely loving the new tab-stacking feature (just drag one tab on top of the other to stack them). I sometimes tend to open a dozen tabs while checking a single page's links and this will allow me to regroup them. I believe it might be a bit more practical than Firefox 4's projected whatchamacallit tab management window.