Unfortunately, I'm probably one of the few Pre owners that will run into any problems updating their phone to WebOS 1.4, which was released just hours ago.
The "updating" throbber froze at just over 1/3 complete, leaving me with a completely still screen telling me at the bottom "Installing Update Do not remove battery". Crap. After giving it another 20 minutes to make sure it was really stuck… it was.
So I did exactly what it was telling me not to. I opened up the back cover (and was surprised by how much dust had accumulated inside my phone), pulled out the battery, put it back in, and turned the phone back on.
And it worked. The Pre went right back into the update process and a few minutes later was already past the point where it had originally frozen.
So, if anyone else has this problem, and the throbber isn't even spinning. Try yanking the battery.
If that doesn't work, you can try the webOS Doctor available from Palm's website (webOS Doctor [palm.com]). webOS Doctor will completely wipe and restore your phone to the latest webOS version, this means you'll lose any pictures and media you had on the phone (try mounting the phone in USB mode and downloading all files before doing a recovery). Your contacts, calendar events, and tasks will be synchronized with your palm profile.