There was a similar issue with Snow Leopard and I would not doubt others had it with Lion. What irked me in my case was my first year i5 iMac (the i5 in twenty seven inch form) was perfectly fine until I upgraded. Then suddenly wireless may or may not work upon waking from sleep. The odd part was, it might work for a few seconds after waking before I would have to manually end it and connect again. It was talking to the Airport Extreme just fine, it could not get beyond it.

The kicker, the copy of windows which I ran through Parallels could connect. I could surf sites and VPN through Windows in a VM while OS X applications could not, until I bounced the wireless connection.