I am having the same issues as others. In the last 2 days my phone has completely frozen 4 times. All but one of the freezes have been related to some sort of sms function. The first of the freezes occured when I was playing a game of angry birds, and I recieved an SMS popup alert. The second happened in the middle of using the stock text messaging application for a simple SMS reply. The same with the third freeze. After each of these three freezes, the phone automatically rebooted itself.
After becoming frustrated with the issues, I factory reset the phone today. Not an hour after my factory reset, while configuring Beautiful Widgets (current version, freshly dl'd from the marketplace.) the phone froze. I then tried using the sleep button to escape the hiccup, after the home and back buttons would not work, but the phone was completely "dead". The phone was completely unresponsive, with a blank screen. I had to perform a battery pull to revive it.
I have also had a few occasions where my 3g was supposedly working, but I was unable to use data. The 3g icon and signal strength were at the top of the screen, but when I tried to use the browser or marketplace, I received connection errors.
At this point I am at a bit of a loss. I am beyond my 30 day window of return. I have been extremely meticulous with the care of my phone, and I do not want to get rid of it for a refurb.
I am really hoping after seeing the number of people with similar issues, that the real issue is with the firmware on the phone. I'm really looking forward to the official Froyo (2.2) update, to see if I will still have these similar issues.
It is rather disappointing that the many droid X users (including myself) are having issues like this. The X is supposed to be the absolute best phone on the market right now.