Issue with Samsung Galaxy S2 (phone constantly reboots)

I've noticed a major problem with multiple Galaxy S2s I own. In the middle of use, they will simply turn off and reboot themselves. This can happen 15+ times a day sometimes, and then not happen for a few days, or even a week.

After some very brief searching, it appears as if this is a problem that a huge portion of the user community has encountered. Samsung claims to know nothing about the issue. I find this hard to believe, as many of the posters in the threads found during a search mention contacting Samsung about the issue.

Here is a tumblr documenting 75 of the first related links coming up during online searching:

Tumblr

Has anyone else here experienced this or know anything about it?