I replaced the screen/touchpad a month or so ago. Works great now and is a bit brighter. My 550 is about 6 years old and has been beat around pretty well. Never had a problem with it. Use it for routing, MP3s, XM, and bluetooth for the phone.
I have gotten my money's worth. The 665 will be next if the 550 ever dies.
BTW, I almost always carry paper maps with me just in case.
RR