Regular shaking of cartridges is recommended at Inkjetmall. I just give the printer a bit of a jiggle every few days. I'm hoping to avoid my 3880 going the way of my 3800.
If you don't print anything for 6 months or so then perhaps it's an issue and the inkjetartmall article has some merit, but really the printer has enough vibration to keep things sufficiently suspended. If you use it so infrequently you need to shake it, you're going to have more problems than just pigments settling out.
As an aside I was curious about this once so I actually opened an expired two year old 3800 cartridge that had been sitting on the store shelf and carefully poured it out over a large sheet of plexi. I assumed if the pigment's had settled out I would see some density or color shifts in the ink. Could see no difference anywhere, no real sign of anything, and density and texture of the ink didn't appear to change at all. Not very scientific and doesn't prove anything, but of course had I seen a difference then it would have. Additionally it might have just shown that just the movement of the cartridge and process of opening was enough agitation to resolve settling.
I've never seen any documented proof the pigments settle out enough to cause a problem as long as the printer gets some use. Other than Epson recommending gentle agitation before installing new cartridges (which could easily have been sitting motionless for 6 months to a year or more) there is no recommendation from Epson to do take them out and agitate them and despite the articles conspiracy theory that epson just wants to sell more ink, it could be they actually know it's not an issue.
But I have seen printers with problems with leaking and damaged ports from people who for some reason think they needed to take them out and shake them every couple of weeks.
I really think this is more of a myth that has stayed alive since the 76/9600 printer, sort of like the need to fully discharge a battery before you recharge it if you own a current laptop with high quality lithium ion batteries which is a leftover of nickel cadmium days.