I've an N97 and a (loaned) N900. Stuff I've been up to with mine @ http://doitdifferent.wordpress.com It's good, but the N97 is a better phone/sat nav, and can be used one handed. Sure the N900 is flashier to use, less "clunky" but it's maybe not as good a phone. Depends on what you need your device to do though.
On a recent trip, I put my simcard in the N97, but took the N900 instead of a laptop…
I'd not recommend an N900 to everyone, but depending on your needs/how geeky you are, it *is* a great option for some.
Nexus one also worth a look, if you can see past (pun intended) the screen (unreadable in the sun) and grim camera.