For a few weeks now I have been seeing weird network behavior, but only at home and only on my Macs. Both Macs connect to a WRT150N wireless router running DD-WRT VPN firmware. As described in an earlier post (its early and I am too lazy to link) I have set up a fake TimeCapsule on an Ubuntu box sitting on my home network for net-based backups. Everything was working fine until a few weeks ago...
Suddenly when attempting to move large amounts of data across the network, such as when backing up, my network connection would drop. My connection to the network remained, but throughput went to zero on the local network. Connectivity was completely lost. Many times I couldn't even reconnect to the wireless network to reestablish connectivity. However, if I used a hard-wired connection I didn't see the same problem. Ultimately this corrupted my TimeCapsule data twice in 2 weeks.
After some frantic Googling I found somewhere which indicated that the problem may have to do with auto channel switching in 802.11N networks. So last night I configured my wireless network to choose a specific channel (8, FWIW) instead of allowing it to automatically choose the best channel. My network problems appear to have now been resolved, no more loss of connectivity over night or this morning. I created a local backup on a USB disk overnight and I am now recreating my online backup to the Ubuntu TimeCapsule as I write.
This seems to be an unacknowledged bug in most recent versions of MacOS Snow Leopard. Apple, I hope you're listening.