Well, alghough I have about 4 Symbian phones I use Samsung D900 on everyday basis. Here the small list of advantages and disadvantages:

Advantages:

+ Size
+ Screen
+ Battery life seems to be ok 3-4 days
+ Simple & Fast Interface

Disadvantages:

- Having a 3MP camera with autofocus is useless, it is so slow, about 15 seconds to make a shot (your objects cannot be moving as well)
- No option to set your own tone for sms
- No option to set different volume for ring, alarm, sms
- No auto save to sent folder
- Only 200 sms, and always the first 10-15 sms saved on your sim card
- No automatic Alarm for birthday settings in Phonebook
- Very inaccurate PC Synchronisation
- Poor Java support (cannot access camera API, cannot even run GMail Application)

But still quite good, neat machine and doesn't take space in your pocket. If I would buy a phone today I would probably go with Nokia 5500 or Sony Ericsson Z610i in non-Smartphone Market.