In my 15 years flying professionally I've experienced severe turbulence only once, following a really nasty windshear go-around in a horrendous storm back in 2000. Neither myself or the FO could read the instruments, the autopilot threw it's hands up and the aircraft was briefly uncontrollable (5 or so seconds) on several occasions before we were spat out of the turbulent area. My PA later was along the lines of "Well, you all enjoyed that about as much as I did.. my professional involvement with Gatwick is over for tonight, we are going to Manchester now where the weather is MUCH nicer."
Most bad turbulence is moderate, but perceived by some as being severe due to lack of exposure. Passenger and crew perception as always worse than the guys at the sharp end.
And another thing... please realise there is no such thing as an "air pocket." Air is a fluid, just like water, and behaves just like water. You expect waves on a lake or a river, and if you look at the edges, or around rocks, you will see eddy currents swirling back on themselves. It is exactly that sort of fluid behaviour that leads to turbulence, not some lack of support from the air itself as is perceived.
Squid