A couple years ago my 125g sprunk a leak without warning, along the bottom seal.
It was about 11pm one night and I sat down on the couch to watch a little TV before going to bed, and looked over at the tank. The water level was about 1-2" lower than it was earlier that day...
"Strange," I thought. Then it dawned on me....my heart sank.
I jumped out and flung open the cabinet doors of the stand....water gushing everywhere, and of course, all over the power strip. Without thinking I immidiately hit the kill switch on the power strip (lucky I didn't get zapped).
I was real lucky. I remembered my neighbor/friend nextdoor had an empty 55g tank he didn't have set up. I called him as I was siphoning water outside and he brought over the 55g and I set it up on my coffee table and filled it w/ water from the 125g.
Spent the rest of the night breaking down the 125g and drying the carpet. I didn't lose any fish (had at the time a 10"+ Oscar, 6" jaguar cichlid, 7" pleco). I had them in the 55g for a full week before I could buy a new 125g (I didn't even want to consider re-sealing it (as I have no experience doing that) and I didn't even want to think of the possibility of another leak, so I just bought a new tank).
I still don't know what caused the leak, but I have a pretty good idea. The first year the tank was setup, it was on a custom stand (was setup in front of an old fireplace that didn't work) so it had to be a custom built DIY stand. Well the tank didn't sit perfectly level, and I think that factored in to it leaking. After the first year I moved and set the tank back up, but with a store-bought stand this time (since the custom stand was only useable at its original location). I think it warped slightly over time which eventually led to the bottom seal giving out.