The main advantage is that companies like Epson use such patheticly small cartridges, and also if a cartridge runs out halfway through a large print you lose everything (mostly because of their silly software)
A continous Ink system solves all these problems in an instant.
In my experience if you go for a quality CI system, such as Lyson, then when it works its absolutely fantastic. I think it should be how the factory build the printers, but they can be problamatic, and then they become a right nightmare in terms of spending a lot of time getting them sorted again before you can get great results once more.
However I'm told that the newer Epson models such as the R1900 and R2880 have much less problems with CIS as they have a much stronger pump for pulling the ink through.
Paul
www.photographybyriddell.co.uk