I've had the 7900 for about a month now with no serious issues. The printer sometimes gets some clogged nozzles if it sits for a week or so but they clean without problems. There are a number of things I was worried about because I read about them online, which seems to be what has you wondering. Some "problems" are just normal and not the result of any defect. For instance, when you first install inks and charge the lines the printer will use much more of the light gray ink than any of the others, and about 40% of the maintenance tank capacity. This is just how the thing is designed to work and it should happen only once in the life of the printer, when inks are installed for the first time. It's not a defect and there's nothing to fix. I have some very odd problems with the software that updates the printer's firmware. Something is definitely wrong there and others have reported it too, on both Mac and PC, though it doesn't seem to happen to everyone. The bottom line is that the firmware does get updated so it's really only an annoyance.
Basically, I think you'll really like this printer. It's very easy to set up and use, and the output is truly stunning.