Triangle ink here. Lots of it. Our XC's been on Triangle since about two months after we bought it (five years ago), and our XJ's never seen Roland ink in its four year life. Between the two machines we've gone through about seven heads (all but one of them were WAY over the 6 billion shot expected life. The one that was short had a few bad head strikes, and was at about 4.75 billion). Before we bought our two HP's, we were going through 6-12 liters per color every four weeks. That's 36-72 liters a month. That's $4104 for Triangle ink that would've cost us $9736 in Roland ink, figuring on 36 liters per month.
I can't wait until Triangle figures out how to get around the issues they're having getting latex ink to work...
Also, let me state as I always have, that if you are not doing some serious volume, do not switch to third party inks. I wouldn't recommend it for anyone who is not using AT LEAST a liter or two per color per month. But if you're moving some volume, the savings are significant and the problems mentioned above won't exist, as long as you're using a quality ink.