So far I have nailed down 3 things happening... (yes, I posted this in a few places to help people with the problem, and yes, I experienced all 3)
1. Phone loses activation. This is rare and resetting your connection does not fix it, try the Activate button. I had a bad rom flash do this to me, but others have had it at random.
2. 3g drops due to loss of connection and using an app or setting to increase battery. There is speculation that the menu is labeled wrong on our phones, creating problems. personally, I wiped and got rid of all connection manager type of stuff and leave it stock, it works fine. Fix the other things robbing your battery like Twidroid and Gallery running in the background.
3. The browser.
Dolphin mini has been reported to have connection issues, and I confirmed last night that HD has the same problem. Everything worked on the phone, except for it. I reset data, and it came to life. Do NOT use Dolphin to check for connectivity. If it's your default browser, change the home page to a more reliable site like Google or Yahoo, it may help at least some.