I moved my home office today and found that my mac was no longer able to connect to my 5GHz 802.11n wifi network. Turns out it was likely an issue when I installed OS X Lion, I just didn't notice the network selection problem because a) I've been traveling, and b) I use a dual-band router with a 2.4GHz 802.11b/g network as well. Hunting around for a solution that worked for me took a while, so here's what I tried, in case any intrepid google-searchers come across this.

I was getting an error that a "connection timeout occurred" any time I tried to select my 5GHz network. Per advice online at Apple's forums and elsewhere, I attempted:

• resetting the router
• resetting the password
• changing the encryption to WPA2 rather than the WPA/WPA2 my Time Capsule offers
• deleting keychain items for my wifi networks
• deleting networks from my preferred list in Preferences
• moving my router
• resetting the computer

None of these did anything. From an old forum about a different issue entirely, I read a suggestion to set the router to manual channel selection, since a router in a crowded radio environment can hunt for an open channel too rapidly to form a stable connection. Upon changing this in my Airport Utility, the 5GHz network again became usable on my Mac. Huzzah!