FreeByrd:
Your overboard experience sounds a lot more interesting than mine, parrticularly since my motor was in neutral. I'm not sure how much fun it would have been to reboard if the prop had been turning. Thank goodness for your friend's advice to drag a rope.
As to the inflation, I use the three-way vest: blow on the tube, pull the handle to activate the CO2, or automatic activation of the CO2. Here, the vest inflated automatically, via the CO2 cartridge. The operation was almost immediate upon immersion, and very sudden. Darn near lost my glasses.
The suddenness and extent of inflation of the vest underscores the manufacturer's caution to not wear any clothing over the vest. If you have a jacket on over the vest, and it inflates, you aren't going to have any time at all to unzip, and are probably going to have a severe, and possibly terminal, breathing problem.
The other thing which surprised me was how difficult it was to bleed any of the CO2 out. The vests are designed to keep your face out of the water, and do so by inflating to a greater extent whan I had anticipated. Once you figure out that you are conscious, you want to let a little of the gas out to make it easier to swim, deploy the ladder, and climb back on board. Although I'd unpacked the vest several times, and plaid with it a little, I wasn't able to bleed it, either while in the water, or for a while back on the boat. Then I finally figured out what to do, and it's simple. The bottom line is, practice, practice, practice. It doesn't hurt to open these vests up a couple of times a year, inflate them by blowing on the inflate tube, and then deflate and repack.