I've been running the developers program since April. There are only a few things I am missing.
1) My wifi calling works, but wifi texting does not.
2) I have a fitbit and can't use the phone since the Cyan update brings the low power bluetooth.
3) There was a new caller ID program re-released last week that doesn't work because it needs Cyan.
Other than those things (for me) it is working really well. I really like the notification center (I didn't think I would cause of the live tiles) and don't miss the Me tile functionality as much as I thought I would with the facebook app either sending notifications, through email or the live tile getting updated.