They'll probably get all of the debilitating bugs that result in the quests coming to a screeching halt or issues w/ crashing but leave the smaller bugs for another patch. No offense to Bethesda or anything but they really should have picked the beta testers to those who have been on the forums longer than 5 minutes so they could possibly avoid a majority of the free loaders.
Forums aren't everyones cup of tea. I'm sure there are many good candidates for bug testing who don't bother with forums. On top of that, im sure that between questionnaire answers and forum input, most freeloaders would have been weeded out.
Going by the apparent amount of 'I dint get da beta' butthurt which apparently followed the emails being sent out, I'd say they did a good job. Not to mention a couple of the guys they chose gave me immense confidence in their selection policy.
Will it be buggy? Of course, but it's one of those things I think we'll have to accept as gaming gets more and more advanced - new stuff will be buggy.