TOO vigorously, as I've discovered in my first two all grain brews.
I bought a bunch of new gear all at once, including a 10-gallon stainless pot that is much wider than my previous kettle.
I just finished pitching my second all-grain brew, and I started with 6.5 gallons pre-boil and after 60 minutes was under 4 gallons. I use a propane burner from a turkey fryer and I've always heard that "more boiling is better" but in this situation I think I was boiling way too vigorously and need to tone it down a bit next time.
The mash and everything else pre-boil were perfect, all gravities within 20 points of target, but after the boil everything went to crap, including dropping my "wine thief" into the carboy where it will remain until I rack to secondary...
But the important thing is that I've learned my lesson and won't run the propane valve wide open next time; I'll show a little restraint and look for a rolling-but-not-out-of-control boil.