I think my record was on a very cold day in the Summer, idk the exact amount of hours, but I think about 4-5... *EDIT* it was actually about 8 hours... I didn't want to make it look like I had no life (I don't btw)
Actively in-game or just in-game? If just in-game, over a year ago I probably spent 2-3 days straight online... at least twice. I used to leave the game open. Was long before chat logs really existed, and I was always curious about the current discussions. And at the time, there were huge periods of time between messages... xD Actively playing, I've likely done 12-14 hours, but it was a long, long time ago.
I played once for 34 hours straight, not doing much though, just Moderating chat. If I think back, it was when Andrew went to Minecon, so I thought i'd look out for anything that may blow up the server.
Me and my friend have actively played ECC for 12 hours straight at my house. 9 in the morning to 9 at night . We ate while we played and we brought our laptops to the bathroom if you need to know that.