OK, here's mine:
The main one was with a very early model Ikelite 10D housing, probably on about it's sixth dive. I was at 45 feet and lying on the sandy floor to try to shoot some subursts - and then noticed water trickling over the viewfinder from the inside. Made a pretty (very) quick ascent and swam back to the boat with the housing above my head. Camera was definitely wet but - somewhat suprisingly - survived to shoot another day.
Back then I was very fond of my shiny new 10D so I always made sure there was no sand etc on the rear o-ring (was pretty obsessive about this). But we'd had humpback whlaes swim under the boat on the way out so I'd grabbed my camera out of the housing to try and get some shots. I think the most likely scenario is that my hastier-than-usual reassembly once we reached the dive site left some dirt/sand/etc on the o-ring.
I spoke to Ike about it and - as always - he was great with the customer support. I had a new housing shipped to me immediately whilst he pressure-tested the flooded one and was back shooting in no time.
Back in the day - before upgarding to the Ikelite housing - I was doing my underwater photography (with my precious, new DSLR and 'L' lens) using a EWA-Marine bag, It survived lots of free-diving and some SCUBA to pretty decent depths with no problems whatsoever.