I take pauses that can last months, but Istaria is home.
I play(ed) many MMOs but when I talk of my "main" I imply my dragon and in Istaria.
In fact if one day someone told me "Istaria has closed" I'd look at him like he said that the sky is not blue any more.
Now, if only we could get a graphic revamp (at least to players and dragons, I don't care if golems become shinier ;P) and the mobs AI was more challenging... I'd love Darkfall AI in Istaria, it's PvE but almost as challenging as PvP (ie the challenge minus the jerky mindset of "hardcore" harassing PvPers.