I have had the same thing start to happen with my 60CS in the last week or so. The only button that works is the power. The unit is not locked up because it is still tracking and showing pop-ups for turns but I cant get it to respond with the keys (other then powering it down). I have had to shut it off and press all the keys really hards a few times then power back up and keep doing this untill they start to work again. I am going to call Garmin in the morning and see what can be done.
The big problem I have is I use it for work and even being without it for a day will be a HUGE pain. I have a GPS V as a back up, but I am really spoiled now and do not want to go back to the "old" gps. I have also thought about getting a Quest for work but I still dont know if it will be worth it.
I too have had my 60cs lock up while using the cityselect V6 Oahu maps. Garmin was so kind to send me a replacement unit which also displayed the same problems here on Oahu. I took both units to Colorado for a 10 day vacation and both worked perfectly. This leads me to believe that the problem lies with the map software for my area only.
I updated my 60cs to version 3.61 last night and I hope this solves the problem. I will keep you posted. CL