While 12 weeks is ideal, there are many of us who have brought home puppies before that time for a variety of reasons. You are going to be in for some more work with things like socialization and bite inhibition, so start your research now to help you avoid some frustration. Potty training is going to seem to take f-o-r-e-v-e-r, too, just because he's too young to hold it for more than about an hour at this point.
Remember, too, that because he's going to be younger that he will tire more easily and be more prone to developing hypoglycemia. Short play sessions, food available at all times will help you avoid that, but know the symptoms and have some nutrical/nutristat (ultra mega high calorie booster from Petsmart) handy.
His immune system isn't completely developed yet, so hold off on taking him out in public where he could be potentially exposed to all kinds of dog germs until he's at least 2 weeks out of his last round of puppy shots (those usually finish up at around 16 weeks). I know that one is hard, everyone wants to show them off while they are so small and cute
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Oh, and I have to heartily second the poster who said to ask Mardelin if you run in to problems. Her knowledge is gold! She helped me immensely when I got a rescue puppy who was too young and didn't even have any teeth yet!