I bought our 3800 in November 2006, it was one of the first available in the UK, and it still has three of the original carts installed.
I pulled them all out last year when changing a cart and gave them all a shake, but I've not noticed any deterioration in print quality since new. I rather hope that the automatic agitation technology Epson boasted of when they first launched the 3800 has a lot to do with it.
I've also only ever had one nozzle clog after a particularly heavy head strike on some thick art paper in the first week of use. Since then it's been faultless despite it's lower than anticipated usage.
If I was bothered could go back to the original profiling targets I printed and compare them with a new set.
When first released Epson claimed a six month shelf life for the 3800 ink carts, but in my experience that's hopelessly pessimistic, or a marketing ploy, keeping carts beyond the six months date is absolutely no problem at all.
With respect to 'calibration';
As the 3800 is one of Epson's professional range, it is accurately calibrated on assembly. It's very unlikely to need re-calibration until you've used several sets of ink carts or several years have elapsed. Calibration can be done with the Colorbase utility, downloadable from Epson, but you'll need a supported spectrophotometer like the GMB Eye-1pro to measure the print outs and generate the calibration file.
In theory keeping the printer calibrated ought to ensure output doesn't change and any custom printer profiles you've made, or bought, should remain accurate. My profiling business(http://www.colourprofiles.com
) will support clients with the 3800 by measuring Colorbase print outs if required.
Unless the printer is getting a heavy daily workload it's probably not worth worrying about unless output significantly changes or the machine is serviced (which ought to include re-calibration anyway).
If you're using non Epson papers it's worth getting custom printer profiles made as some of the profiles supplied my paper manufacturers aren't as good as they could be, but Epson's supplied profiles work well for their own papers and may be all you ever need.
Hope this helps