I have one of these fine printers - the older 3800 - and thought it might be interesting to see who else here uses one and how they find it.
I don't use mine enough and the inks are way out of date now, but it still seems to work pretty well. When I haven't used it for a while I always stir up the inks before I print - just pull each cartridge out and give it a bit of agitation. I've had to do a full on head clean once, which uses a terrifying amount of ink, but I think it's a small price, overall, to pay for such outstanding print quality.
There is a great 3800 resource here, run by Eric Chan who I think works for Adobe. Everything you ever wanted to know, plus some really good profiles for use with the Advanced Black & White function.
For those considering buying one, I think it is important to remember that you will need to be doing a fair bit of printing to use the inks within their use by date. This is much more of an issue with these than cheaper printers because the cartridges are huge. They're expensive too of course, but much cheaper per ml than anything with those little 20ml carts.