I have had my N93 for a few months now. The power button always worked fine, when I pressed it it always displayed the profile menu on the ouside (2 lines of text, controlable with the outer joystick). It absolutely never failed.
After these few months I noticed the phone got slow without any warning. One day it just simply woke up slow. I mean slow. The menu button could take as long as 2 minutes to take me to the menu. Starting a new SMS message could take as much as 1 minute. And various other slow operations like activating the camera and many others like redrawing (which made the display look corrupt).
I took a look at the process list and it was huge. I took out the memory card and restarted. It seemed fast again (not as fast as when I bought it, but much faster anyway). I formatted the card (all applications on it were lost including various games and tools). Never mind, it was for a good cause.
It worked ok for a few days (no significant delays in operation), then it started to get slow again. Not as slow as before, but slower anyway. I remembered how it seemed fast to me when I bought it when compared to my (previous) 6630 (more than twice the speed when going through menus and messages). So I compared them again, the 6630 won.
So I checked for a firmware upgrade. No use, I already had the most recent (20.0.058). Nevertheless something had to be done. I upgraded the firmware anyway (to the same version, so not really an upgrade).
After it was complete I was again amazed with how faster (than my 6630) it is. It seemed to completely recover speed up to the original (the fastest I had ever see it go) even with the memory card inserted. I was happy.
This feeling lasted for about 2 days, since I have just now discovered that I got the power button bug. I am now unable to display the profile menu on the outside screen. And, as already described in this thread, when I do it it is being operated on the inside (the external joystick doesn't work). This is very anoying since I had already grown acustumed to it in movies and the like.
I don't know what to do. It seems like you guys already gave up, since the latest post dates back to 2006. I checked the version I installed, and it is also the 20.0.058. Maybe I'll take it to the shop tomorrow, the waranty is still valid.