Hi Glenn,
Since my first wide format Epson printer(7600) I have never been a fan of agitating the installed ink carts. As I noticed immediately the first time I fired up the 7600 and printed a file, the printer itself creates more than enough movement to agitate the carts without further attention. When I bought the 9900(2010) I was somewhat doubtful that action would still be present, due to the heavy duty stand. The first time I ran a print on it I placed a small container of water on the end deck next to the control panel. The activity in the water answered any questions I had concerning the possible lack of efficient agitation of the installed carts, more that enough activity. As far as stored carts are concerned there might be a case to be made for a gentle a agitation cycle occasionally, depending on the elapsed storage time. However, I have never agitated a cart until I am ready to install it and there has never been a problem. Referring back to the fact that the printer on a its stand will provide efficient agitation; in my opinion there is definitely a case to be made for occasional agitation of all carts installed in a printer on a rigid stand, such as a bench that may have been constructed for that purpose. The OEM stand is constructed in such a manner as to allow for a certain amount of "sway", therefore agitating the inks as well. One other thing I have to mention. It always makes me cringe when I hear or read someone offering advice about "shaking" ink carts. Absolutely the wrong approach! I believe one should never shake an ink cart for any reason. That sort of activity can very easily cause more problems than it could ever solve. A very gentle back and forth agitation in all four directions is all that is required. Of course that is indeed simply my opinion, and one I have always followed with excellent results, for what it's worth.
Gary