The cost of the device, which started from 24000 INR is down to around 14000INR, that tells about it's sales figures.
I heard it otherway around..it is Nokia's best selling mobile phone alongwith E63 or E61(i don't remember clearly) for 2009 despite the fact that there was some problem with sound initially.
I bought 5800 on 10th nov..i found its UI is pretty lame in front of my 1.5 year old itouch..but once you are over with it rest are very good.
About music quality, its sennheiser headphone (comes free with the pack) is best..the built-in speaker is a bit..well,quality is very good,but not lud enough..my 3000 rupees SE phone that i use as a back-up is louder.
I short listed n79, 6700 classic , samsung touchwiz and 5800xm and after a week of going through a lot of details i bought 5800.
1 pet peeve : the battery drains out like nothing i had seen before, in 20 hours or so..but can't tell you if its my phones battery or the 5800 batteries in general that has this problem