So I haven't seen anyone mention this specifically (although I admit I didn't read every post in this long thread), but I believe the culprit (at least on my phone) is
Swype. I was only having reboot issues when any app invoked the GPS (Foursquare, google maps, sprint nav, etc). I did a factory reset and then installed apps one at a time and tested google maps & sprint nav to see if it would reboot. I would manually power down and back up then test again to make sure everything had loaded correctly. No issues at all over the course of a couple days until I re-installed the Swype Installer which, once installed and opened downloads the newest Swype Beta. Once that was installed and opened, any time GPS was activated my phone would reboot. I uninstalled Swype, but still had the issues. So I did another factory reset and have loaded almost all of my apps back onto the phone (minus Swype) and have yet to have a single reboot!
YMMV, but for me and my EVO, no issues at all without Swype. And trust me I don't work for some rival company trying to diss Swype...I miss it SORELY, but what I don't miss is having my phone reboot constantly. So for now, my EVO will be using only the factory keyboard input until I hear that Swype has been updated to correct this issue.
Here is the list of apps I had installed on my phone that I'm still in the process of re-installing to ensure that none of them are the culprit as well.
club619's Apps on the phone
I'll repost if I notice any other issues. One other thing I'm thinking of doing is performing another factory reset and installing only Swype to see if it'll cause the reboot with no other apps installed (other than Astro File Manager...not sure how to reinstall it without that app).