I bought one not long ago, around 2 weeks maybe. I had an ETEN X500 before, thats a PPC phone. The 5800 is a dream come true after windows mobile. It's fast, looks good, has GPS, wifi, and dedicated audio chip. The only downside is the cheapish plastic body. It won't be raspy, since the build is quite strong, but the plastic used as the body is low quality. I spent 2 days to make it work on Vista64, windows couldn't recognize it, tried tons of drivers and softwares and finally made it work. There was no problem on win7 and vista32 tho.
The camera is ok, if you use it in daylight, but totally useless when it gets a bit darker.
GPS is damn fast, gets the signal in few seconds, and never loses it. I use the Garmin Mobile XT. Not bad, but the IGO for symbian will be better.
By now there are many themes and apps modded for S60v5, so it won't be a problem. I don't know if you know how to sign unsigned apps, you will need it I think, cause many apps are unsigned, and need to be signed in order to install them on the phone. there are many tutorials on the web about it.
Touchscreen is working very well, even when you are browsing, it's really accurate. It supports muli touch, there are some games that use multi touch, but symbian doesn't use it, afaik because of the licensing issues. But there is no need for it.
About battery life. First 2 days it only lasted a day or so, but now I get 3-4-5 days out of it. I use GPS around half an hour a day, then MP3s and some sudoku, so the battery life is ok.
In overall it's quite a good phone. Good sound quality ( i find it a bit quiet with the factory headset tho ), the 3,2'' 640*360 screen looks awesome, but it's a bit hard to read in sunlight. Never had Nokia before, but I didn't regret it. It's not as exclusive as an iphone (which I personally don't like) but does everything what an iphone does.
It came with an 8GB microsd, a rubber case, spare stylus (which you will never use), headset, usd cable, a pick (you can use it instead of the stylus) and a funny looking holder if you want to put it on a table. Took me 5 days to figure it out what it is good for