I get this issue as well. Been tearing my hair out trying to diagnose and fix.
Basically, my home wifi doesn't work. I'm resorting to turning wifi off and using 3G.
Specifically it appears to be applications I have to sign in to that have trouble connecting - mail, twitter, facebook, yammer etc. Safari itself is slow, and rather hit and miss, but I can get web pages to load - often requiring several refreshes. Those other applications time out constantly.
Wifi at work is no problem. Flawless.
I take it from that it's a router issue, but I can't find any magic setting or any information online that tells me where to look.
Frustrating to say the least.