I upgraded daughter to one of these Galaxy S 2s. As she's away at Uni, it is still mine to play with. Not had any such problems. I'd get one myself, but it doesn't fit into my pocket.
With my (much cheaper) i5800, (with a different 'droid number) though, proximity to the wi-fi source can be an issue. If/when it is, I turn off the wi-fi on the phone, and turn it back on next to the (BT) wi-fi source. That normally keeps it happy for a while.