I too own the phone clicked some nice pics.
I havent upgraded the firmware though and it is same, as in february when I had bought it, had checked at that time there was no new firmware update for it.
It is very stable has not give me any kind of problem yet, though have not checked much of its music features. ANd I love its blue backlight, battery I can say is low in comparision to nokia which use BL-5C. for K550 battery goes low quick now, unlike earlier when it ran for almost 2 and half day lasts for 1.5 to 2 days(may say due to increase of usage) but certainly the display takes alot of battery.