Wayne hit the nail head with everything. I have a print from an I850 taken with a Canon G2 and I prefer the same picture printed with my 6-color S800. But you have to decide if you really need an all around printer or if photos are more a prioity.
I have made a print with the I70. I took my G3, a piece of Photo Paper Pro, and USB cable to Staples and connected it to the i70 to try the DirectPrint feature. I was not impressed with the output; it appeared to be overly exposed and washed out, to which the original image was not. Also, the ink tanks are small and expensive for how little these tanks are. I think they are between $15 - $25, black being the less expensive.
i think the i70 would be great for general printing purposes when on the go, but not for worthwhile photos.