Hello---we have a P-800 at our college, as well as two 3800's, one 3880, and one 9890. I have used only OEM ink so far in all, but use IJM carts with PiezoFlush to clean all but the P-800 out, and for extended periods of storage. I realize now (but not when I bought it) that the P-800 has so far proven impervious to the use of any non-epson cart, so I can't continue this maintenance routine on it.
We have only 4 months of use on the P800 so far, and it seems reliable---no propensity to clog, unlike the 4900 we gave up on. We operate at temps from 66 to over 80˚, and whatever humidity southern Vermont wants to treat us with. I remove and shake carts every 1-2 weeks. During term-time, the machines are "on" about 15 hours/day, with varying amounts of use.
What have other users experienced with a P-800? I hope a few IJM fans & customers exist that have P-800's....If I had known about Epson's hard-ball tactics, I would have bought a refurb'ed 3880. Our existing one has been very reliable and trouble-free.