I think it's a 5.1 issue. One thing I've noticed is in my bedroom, where I'm on the fringe of my wifi coverage, that both my 4S and iPad 1 have much less, if any wifi signal, than they did before 5.1. Before 5.1 I always had a signal, albeit it was usually slow. Now I'm lucky if either remain connected. I've had my 4S replaced because it would drop both wifi and 3G pretty consistently after the 5.1 update. New one still drops wifi from time to time, but 3G has improved with the new phone.
I haven't really noticed any drops with my new iPad, but it still seems a little slower and has weaker signal than I think it should. Slower than my 4S and old iPad were before 5.1.