This thing is driving me nuts! I rolled the firmware back to 7.3.2 and everything worked for a while. One day, the status light on both my AE started flashing yellow and the Airport Utility popped up on every Mac on the network. For some reason. This time there was no way to dismiss it. Cancel out of the utility, and it would pop right back up again. Basically I was in an 'update or else' scenario. Why, or how this happened is beyond me. Anyway, to regain use of the wireless network I had no choice but to update the firmware back to 7.4.1. Like before, it didn't work. I played with the settings for an hour or so and finally got it to the point where my iPhone and iTouch were able to establish a link and had access to the internet. Unfortunately, my Mac Book wouldn't work. I checked and all three devices were set to DHCP. After rebooting the Mac Book it finally started to work, but the Airport Utility tagged the AE's as having a 'self-assigned IP'. On top of that, the IP assigned the Mac Book wasn't even in my network. To make sure I wasn't picking up someone elses WiFi signal, I disconnected both AE's and the signal went away. Connected then and it came back, but still assigning the out-of-network IP. Interestingly, the IP's being assigned the iPhone and iTouch were within the network and in the block of IP's assigned the DHCP server.
I don't have any more ideas how to fix this. Even though I really can't afford it, it would appear the only way to establish a reliable WiFi network is to scrap the AE's and go with another brand AP. This whole experience has really lowered my opinion of Apple. As mentioned earlier, their Tier-2 tech support flat out told me that V7.4.1. killed about 1% of the AE's updated. Knowing this you'd hope Apple would be hard at work to fix the problem with yet another firmware update.