I have the exact same issue :-( But the post above from "prjkthack" solved it!
Although it was my Facebook for Windows Phone that were set for "me only" (and not Windows Phone).
But it's the same solution.
My Radar reboots too
My Radar started rebooting a few weeks back and has done so atleast 5 times to my knowledge now. A friend of mine that purchased the HTC Titan another place expirenced the reboot issue only last morning.