I know about "The New 52," and have heard about a lot of other retcons to handle changes, as well as other reboots. I think I remember, for instance, a reboot of Superman in the 80s that had him as a really strong guy who got that way from lifting weights or something. Someone else told me about a reboot of Spiderman that I think Joe Straczynski did that was about some kind of animal totems, where Peter Parker was chosen or aligned with a spider and there were others out there, too. Some were good, some were evil.
How frequent or common are comic series reboots? Is this done when the continuity gets to hard to keep up with? Does the old line ever continue when a new reboot is brought out so they can run in parallel?
I know there are different situations for different comics, but it sounds like this kind of thing happens fairly often and I'd think it'd be frustrating to watch the same story restart over and over.