Well i am a huge game addict so mine is 54 hours straight.It was worth it gaining 130 lvls total.I was able to get 3 prometheans and a journeyman.Its crazy i played for 2 days straight.
Oh, and I reckon the longest I have spent playing is probably about 4-5 hours. This has been broken up a little to whiz to the bathroom and grab food, but I didn't actually log out or anything so it probably counts :P
I think five or six hours was my record. I got through the last part of Grizzleheim and the first part of Wintertusk. Then I went to cause chaos in Celestia. :3
I think the longest time I've played was the week I was on vacation. I had just gotten like 6 pre-paid cards and had over 500,000 crowns. I unlocked a bunch of new areas and spent most on card packs (which I do mostly) and it was about 12-15 hours. I started at about 8am and played until around 11pm. I was farming, selling, and doing that for about 3 hours cause I love the booster packs so much xD
27 hours. Got a wizard to level 41? I couldn't sleep so I sneaked right by my parents and played. Jade Oni was quite the boss especially for a solo wizard. I need to get my mom to play so I can play longer.
I decided it would be a pretty nice idea to take a wizard to Promethean warlord in one sitting; took me about 2 days(No breaks, had to make sure not to drink too much during this time though), slowing down the most when I got to azteca bosses and when I realized I was getting slaughtered in pvp and made a better pet (was using my orthrus at baby, took about 2 hours to upgrade to a mega sea dragon with pain-giver, 9-4 universal resistance, 9% storm resistance, and spritely). Of course, after this I had a nervous breakdown as is only natural.
I decided it would be a pretty nice idea to take a wizard to Promethean warlord in one sitting; took me about 2 days(No breaks, had to make sure not to drink too much during this time though), slowing down the most when I got to azteca bosses and when I realized I was getting slaughtered in pvp and made a better pet (was using my orthrus at baby, took about 2 hours to upgrade to a mega sea dragon with pain-giver, 9-4 universal resistance, 9% storm resistance, and spritely). Of course, after this I had a nervous breakdown as is only natural.
. Well, the longest I have played without stopping would be likely around 6 hours, for sure! I might have played longer before, but nobody can prove that.
Probably 12 hours. When I used to actually have time for wizard101, I'd just play w101 first thing I wake up in the morning and continue till I go to bed. #addicted
etc
The only time I stopped was when I got halfway through Azteca.
. Well, the longest I have played without stopping would be likely around 6 hours, for sure! I might have played longer before, but nobody can prove that. 
