iMac Dropping connection, others connect fine

Good question. We have a similar problem at our place but the opposite. Our iMacs connect just fine, the MBP can't find the network sometimes. Rather annoying. We are using WPA2 as well, with 2 Airport Express. How about you?

 

The frustrating thing about wireless is that there are any number of factors that could be to blame. I had a wireless problem with my iMac, wherein it occasionally wouldn't auto-connect when waking from sleep. Once I flashed my wireless router's firmware with something more reliable, the problems for the most part went away. Another time, I was getting inconsistent download speeds over wireless; the download would just cut to 0 kbps once every few seconds. Turns out it was a wireless network auditing program (iStumbler) that I had running... it was spamming the console logs with an insane amount of data, seizing the hard drive up to the point where it couldn't devote any time to writing the download to disk. All this goes to say that wireless troubleshooting is notoriously tricky (and that I feel your pain ).

On a related note, in regards to taking the iMac in for service, have you called AppleCare about this problem? They can do a proximity search to find your nearest authorized repair shop. I only say this because when I called, they found a place nearby that I didn't know existed! It certainly saved some time and money, so it's worth getting in touch with them if you haven't already.