I've been having this problem for some months now, and I have been unable to figure out a solution, or even the cause.
At random points throughout the day, my internet connectivity "freezes". I don't get disconnected from my local wireless network. My router doesn't get disconnected from the world. However, for some reason, my computer stops receiving packets. If I'm playing an MMO ( World of Warcraft, in this case, but it has happened with Eve Online as well ) all activity just freezes. If I try to browse, Opera, Firefox and IE all stall at "Waiting for google.com..." or whatever the hostname may be. Inspection with a packet sniffer seems to reveal that there are no incoming packets.
Here's the interesting part.
Disconnecting from my wireless network and reconnecting fixes the issue.
Obviously this led me to conclude that it was a problem with my router or wireless card. However, I have tweaked all the settings on my router that I could think of, including things like QoS, AP Isolation, etc. with no change. My wireless card doesn't really have that many options, and I have uninstalled and reinstalled drivers a few times without any change. Windows Firewall on/off doesn't make a difference.
Anyone have any suggestions for debugging this? It's becoming an annoyance.