Just some personal views:

I really like the N900 and do not regret my purchase at all.

However, the device has some quirks that might or might not be a deal breaker for you:
- Mail for exchange implementation is not ready for prime time
- Syncing Google calendar is difficult, so far I was not able to sync satisfactory ( I need more than one calendar).
- Ovi maps 1.0 is unusable as a navigation tool for me.

Having said that, there are many things that just work without fooling around, like
- Browsing the web
- Skype integration
- Making basic phone calls
- etc, etc.

By the way, I do not have any problems with hardware or reboots at all, HW seems to be very solid..

If I were you I would look at the commitment that Nokia demonstrates to the N900 / platform. Many quirks could be easily rectified with proper software. Nokia is said to bring a firmware update until end of 2009. If they do a good job and improve the device into the right direction for you, then I would purchase. If they come out with something half baked not addressing many problems (or do not come out with an update at all) then I would pass and wait for something more mature.