I can beta. My main squicks would be dark-fic and main character death. I do a lot of SPaG, continuity error spotting, general character and plot detail. Moderately good brit-picker.
I will generally be able to turn around a 10K word fic in 2 days. For longer than 30 thousand I'd prefer some advance notice on the timing, plus 3-5 days depending on level of beta.