I almost bought an N810 but it just was too big for general use. If you are a complete linux fan boy Id see why one would buy it.
Fixed that one for ya
Why woudnt you like the fact that it has additional capabilities (including GSM)? Surely ubiquitous data is a good thing - and the GUI looks rather good too.
Problem with n810 for me is two fold, limited performance and battery life.
***** Warning, 810 complaints *****
It requries you to convert (down scale) videos before it can play them without any lost frames or audio lag, while most webpages are absolutely fine, some which are designed in purely flash or silly amount of java script, handle like a fat man on a unicycle, you got to wait for him to arrive and then make a complete mess while he is panting from being too tired. It just doesn't work, my main use of 810 now days, is music player (there are better and cheaper), note taking, gps and as remote control.
Which is where the problem comes in, battery life. Playing music, only lasts about 6-7 hours, pending how many you skip, if you want to use the net, at the same time, then you get even less.
Now, that could be because I installed one too many apps on there, and one may be spinning needlessly. But even then, to me it just seems not enough time to use it properly for what is essentially is meant to be a laptop on the move.
***** End *****
N900, seems to adress the performance issue, and that is a huge plus from me, I mean technology wise, it is one lean, mean, pocket size machine. And at least according to the wiki, the battery life seems mahoosive, however their claimed usage hours to me seem a bit too unrealistic. And adding a phone chip that is essentially always on state, does not strike me as a good idea for the battery life.
I would much rather have a random cheap phone that is used as a phone/modem, with hours of available "talk" time, with a separate pda, then have both, only to loose both functions at the same time when the battery runs out. It also means you are not a "slave" to contracts, without a need in having the latest and greatest phone, you can easily just use a cheap contract on a cheap phone.
When I moved house and ended up without the net for a few weeks, n810 with my phone as a modem and O2's unlimited bandwidth bolt on for just £7.50 a month, made it very nice and easy to use, 512 kbps anywhere? Due to bluetooth linking, I didn't have to go find a spot with good reception and sit there, to use the net, just plonk a phone there on its own, and be comfy browsing elsewhere.
While I can see one gadget to rule them all approach as the holy grail, practically I am not sure it is feasable per say. And what about the camera? What is the point in it? This, again shortens the battery life, and if you want a picture of yourself, would you really be handing over a £450-500 phone to a stranger?