Two of my friends got HTC Desire (which is similar to Nexus One) and honestly said - as a N900 user I did not like it.

For me pros are apps, responsibility and integrated compass

Cons
- lack of landscape mode :-) (only some applications do support landscape mode), I got used to the landscape mode of N900
- lack of true multitasking
- lack HW keyboard
- locked device (no shell - sure you can jailbreak it and have one)


At least if you are a linux user - don't swap n900 for android phone, you will be disappointed.