OK, I think I may have a handle on this now. I forgot about something else I did yesterday. Now I think there are 2 things going on:
1. The GPS goes to sleep under certain conditions. It might be a time interval, but I suspect it's after an extended period with no satellites in view (that might be why some people don't have the problem - their Pre is near a window or something). You can wake it back up by toggling GPS off/on under the location services menu as I wrote earlier, BUT...
2. Google Location Services prevents the GPS from waking up.
My Pre was fine all day as long as I stopped/restarted GPS when I went back outside after being in for a while. Then I turned Google Location Services back on. All was good for a while. Then I went back into work for several hours tonight. When I came out, GPS was dead.
Couldn't get it to restart until I remembered that I popped the battery out yesterday before I got GPS working. So, here's how I got GPS working again tonight:
1. Go to Location Services/Preferences and stop both GPS and Google Location Services.
2. Completely shut down the Pre and remove the battery, then replace.
3. After the reboot, go to Location Services/Preferences and restart GPS.
4. DON'T restart Google Location Services.
5. If GPS goes to sleep, stop/restart it in the Location Services preferences.
This procedure has worked twice for me now. I have both compass and Google Maps running right now. Hope this helps.