I've had this phone for about a year and a half now, and it's been reliable right from the word go.
The smart-phone functions are great - internet is easy to navigate, and the battery copes well, as long as you don't keep Wifi detection switched on after you finish with it.
Sound is great, and the track playing functions are easy to use, and intuitive. The one niggle I have about this phone is file management - there's lots of space for photos and mp3s (even mp4s), but the software Nokia use is really dodgy. It might be my phone, but I've found it a real pain to use when linking up to my computer - sometimes it won't connect, and at other times, the files are put in odd places.
I find the camera functions difficult to get to quickly - often the moment has passed before I get to take a snap of it.
It's looking a bit worn out and old - the buttons have lost their silver coating, and the coloured plastic underneath is all too clear, and the screen has strange little clumps of scratches where things have rubbed against it when it was in my pocket, I think. Some of the rubberised finish has come of the back, too. But the slide opening still works fine, and all the digits have survived the use very well too.
If you're not going to use the internet via mobile, then you don't really need this phone in my opinion; there's a lot of cheaper options out there these days too. Second-hand, these phones are a bargain though.
It will not charge via the mini USB port unless you have a special Nokia cable.
Overall - a hardy device with a few niggles here and there, but still a classic design.
Edit 20/04/12: still going strong, although the battery has become slightly unpredictable.