I had a play on one at the weekend and the thing which was so noticeable about it for me was the lack of responsiveness.
The resistive screen took multiple (four!) prods to get an link to open in the browser and animation of menus and screens was choppy and slow.
So, while there may well be a decent OS under there somewhere, the impression I got was that it was slow and hard to use.
I don't think enough emphasis can be put on a good user interface experience and none of the other smartphones come close to Apple yet in this area - witness the complaints about the Nexus One's home button being far too close to the software keyboard's space bar.
Sure, they may well boast better hardware spec but that's a fraction of the equation. If the user can't use the damn thing, what's the point?
First off this is an Apple iphone forum. So posts like these are gonna be a dime a dozen. I completely switched from the iphone 3GS to the nokia n900 and I couldn't be happier!
The resistive touch screen is VERY responsive I have no complaints at all. I will admit that coming from the iphone I was not used to the resistive touchscreen, but it didn't take me long to get used to actually pressing on the screen vs. just tapping it.
LMAO i have no clue what LAG this guy is talking about! I have tons of widgets and apps that run in the BACKGROUND and I see no lag at all. If my n900 is able to run snes roms without lag

(also a nice feature is the audio and visual cables included which you can plug into your n900 and play them on your HD TV

also without lag) i'm sure it will have no issues with menu animation.
i'd be more than happy to record a few video clips of my own n900 so you can see how powerful and fast this thing is. The browser is excellent and supports full flash. Head over to maemo.org to find out what the n900 can really do or watch the hundreds of youtube videos as proof of the amazing things this device is capable of. Remember its a computer first with phone capabilities as a secondary feature.
some of the cons I would say is the fact that most of the things you will do on the phone are going to be in landscape. And from what i've read is that nokia is coming out with and update later this month to fix that. The keyboard is a little cramped and takes sometime getting used to. The apps available are nothing compared to the apple app store but then again 80% of the apps in the app store are useless anyway.
i'd be more than happy to get into more detail about the phone and answer any questions I can. But i suggest you do a little more research before making your decision.
BTW i'm on AT&T and only get EDGE, but trust me when I say it's still very fast. Also don't buy into the hype about the nexus one and it's 1ghz processor. the n900 maybe only 600mhz but has a cortex 8 processor which makes it actually faster than the nexus one.