Before I use HTC TyTNII with WM, Maemo is to much better, WM is slow, but I miss good sync, navigation, office, car BT handsfree not 100% work. Other aplication work, but still unstable.
I came to the N900 from an OpenMoko Freerunner... And I can definitely say I don't miss my old phone at all! The N900 may have it's quirks, but it's a better phone and OS stack in pretty much every way...
Before the N900, I used an iPhone (first-gen) 8GB.
As much as I miss some of the apps I've used there, I'm really impressed with N900's supreme geekiness (if there's such a term). And with the possibility of a dual-boot Maemo/Android, I might as well forget the iPhone.
I still use my N95 8GB...fit better in my pockets and....I'm afraid to scratch my N900 so I don't use it a lot....still waiting for the invisible shield...
Coming from Windows Mobile (HTC Diamond), i can only love my N900.
The only thing i prefer on my old HTC is the size. The N900 is too big to fit in a pocket.
The only thing I miss is the N82 camera / Xenon flash quality (and the voice guided navigation :-)
But all in all, I much prefer computer and internet in my pocket thanks to the fantastic N900!