OK - so I've had my Danish N9 for coming up on two weeks now (will be two weeks since I unboxed it this evening).

No spontaneous reboots. Booted it once to start it. Rebooted once a day or so later, just because. Rebooted it 9 days later because it had become sluggish when starting applications. Since the reboot (now 2d 19h according to the Battery Usage app) no general sluggishness. The Facebook app irritates at times when it's off getting updates. I don't have tweets delivered to the notifications screen (else there's nothing but tweets there). Facebook updates and several rss feeds (about half a dozen) there run nicely and smoothly.

CalDAV to Google, MfE to Google (for contacts - only updating once a day) 3 email a/c's fetching email across the day (always up-to-date during the day), available to Facebook, google talk, Skype during the day. Wifi/Bluetooth/3G radios on

The phone runs smoothly and remains a pleasure to use.

I have yet to turn on developer mode - I don't have need of that yet.