Seriously, with my Surround, my first Focus and my current Focus, it just randomly won't turn on. I press the wake-up button, and nothing. I have to pull the battery and start it from scratch. It fires up super fast, way faster than my Android phone, but seriously Microsoft? Why does my phone have to reboot so often?
Since November I have only pulled the battery 4 times (that I can remember) on my Surround. Twice to deal with the alarm bug that was resolved after a hard reset, once after my phone froze using an after market battery, and don't remember why for the other event.
Most, but not all, soft resets (without a battery pull) have been for maintenance, like resetting after uninstalling a troublesome app, making a change using ACT, or testing the results of a reset on the Endpoint registry keys. Since resolving my early alarm issues, probably no more than 1 or 2 unplanned soft resets a month.
It would be good to understand the events leading up to your need for a battery pull, to develop so kind of pattern.
I haven't had to do this for my Focus yet. Of course I've only had it a week. I listened to the WPcentral podcast 117 and one guy on there said he has to pull his battery on his Samsung Omnia about once a week.
Could be a bad app. Could try uninstalling some applications you think may be the culprit one at a time and see if you can figure it out. Shouldn't be the phone unless the battery is bad, but my money is on some application.
I have the notoriously problematic Dell Venue Pro and have had to pull my battery no more than once a month, if that. I do however, have to soft reset two or three times a week, which will hopefully be fixed with the FW update this week.
Oh yeah. Your issue. ;) I would suggest what dtboos suggested. Try to determine when the behavior began and then go to your app purchase history in Zune and start deleting apps one by one, over the course of some days, in the order you purchased them, from most recent to least (tedious, I know). Hopefully, you can determine if that's the cause.
With three phones doing the same thing, it's gotta be the shoes... er I mean apps.