I just updated to AirPort Utility 6.3 and it cannot see either of my 2 Airport Extreme base stations. They are working and I'm online but they simply do not show up in the utility so I can configure them. It just sits there and spins the "working" wheel. Very frustrating. Running MacOS 10.8.3. The previous utility (6.2) worked fine and I used it earlier today. I found a couple of posts in the Apple support community pointing to the same issue so my experience may not be an isolated incident. Not sure of the exact models of AE I have but the newer of the two is 802.11n with dual band and guest network support. The older of the two may not be 802.11n, not sure. They look the same and I am using that one in bridged mode to extend my wifi range on the 2.4GHz network. At any rate, these routers have been in use for years without issues, and the routers themselves work fine. The utility is the issue. I don't have time to follow up and figure out the core problem so I restored my previous Airport Utility to my desktop from a backup and it works fine. Just wanted to alert others to a possible issue.