I watched through all of Gundam Wing once. Yeah, now that I've got the series memorized no need to do that again. Come to think it, I've marathoned just about every Gundam Series(except ZZ which I can't seem to get into, though Puru is quite fun).
I marathoned LOTR extended! 12 hours of "OMG WHY DID I JUST DO THAT!??"
I also marathoned through 3 seasons of Voyager. With college I can't marathon much, but I need to do it with the rest of Voyager, Gundam 00, Mushishi, and *sigh* so much to watch....