But there are things that it does better than the N900. Aside from what was already mentioned by Mikescomputing, out of the box, navigation,
doc editing
MMS support
3G video calling
USB OTG
, are a few tricks it has up its sleeve. There are also IMO better versions of some apps in S^3 like Sports Tracker vs ECoach etc...
In the end, it all comes down to what you need in a device and what you can live WITHOUT and not what you can live with. I find myself in a curious situation because there are times I needed the functionality of one over the other, hence why I carry both devices with me all the time (I have a roaming sim from another country on the N900) since december 2010. I guess what I had hopped the N9 would be is a full combination of an N900 + N8 (=N9), all the goods in each device into one, instead of the "compromised" device that Nokia is now calling the N9.