The *hardware* (everything "outside", not the CPU itself, and excluding the screen resolution) of the N8 is actually great - cool form factor, the quality of photos and videos taken is good, the HDMI out is awesome, USB host mode support - and it has a very good and fine-tuned tactile feedback (although I don't know if this is because of a better vibration motor, or if this is only a software thing). One thing that's missing is the HW keyboard. What's also awesome is that you can charge it not only via MicroUSB, but also with a normal Nokia charger (the one they used for the N8x0) - there is a separate charger hole for that. Not only does it reduce the wear on the USB port, but it also makes it possible to charge your device if you are on the go and don't have your MicroUSB adapter or cable with you.

The N900 still rocks hard from an OS/SW/hackability POV. You can't really beat having a standard Linux userland on such a phone - it's a huge advantage. If the Harmattan device combines all the good hardware features of the N8 with the hackability of the N900, it will be awesome. Now it's just a matter of how locked down the Harmattan device will be (Platform Security). Won't matter for end users (but might have side effects that affect them), but will matter for developers.

Crashes, a laggy UI and other UX problems can be fixed by software and firmware updates. They just take some time.