Luckiliy, I have only managed to dump myself out of my PA once. I was only in 2 feet of water trying to help a guy fishing from shore free a lure in a tree branch about 15 feet from the bank. Being new to my PA, I made the rookie move of grabbing the tree branch as I was floating by and leaning a little too far over the side. The combination of momemtum and weight shift dumped me right in. My PA tipped pretty far, but didn't flip. Thankfully, most everything was stowed. That said, I did test the waterproof capabilities of my Humminbird portable fish finder as it went to the bottom. It still works today.
With the additional height that comes from the seat slider I added since then, leaning too far over the side is something I'm even more careful about today. That couple extra inches of height definitely changed the center of gravity and made the PA feel a more tippy when seated and leaning to the side.
Another word of caution is to have most (if not all) your gear attached to something. Luckily we only lost 1 rod/reel in the lake because we had everything attached!
I actually lost a rod in the Rappahannock River when I knocked it out of my rod holder while frantically trying to pull in my drift shute to keep it from disappearing under a pile of snags in swift current. Thnankfully, it was an old spinning combo I'd been wanting to replace. I hated to lose the rod, but the reel was junk. At first, I thought I lost a brand new combo that was not cheap, and I was pretty angry. This experience opened my eyes to the need to better protect my tackle investments and brought me to thinking about leashes or floats for my rods. Based on recommendations from this thread http://www.hobiecat.com/forums/viewtopic.php?f=26&t=40728
, I bought some of the 8" foam floats for my rods and have been using them the last few outings. I was worried they would throw off the rod balance or get in the way, but neither concern has been a problem at all. I haven't actually tested them to see if they work, as I don't want to submerge one of my good rigs unecessarily, but I'm going to sacrifice an old rod and reel on my next outing to see how they function.