This is all dependent on the 'look' you are after. I am weird and HAVE TO cut my stripes, dots, repeat prints, plaids etc. exactly on the print. But that's just me (I usually don't buy them I obsess so much!). Although the ideal is to cut the fabric exactly on grain, cutting along the print usually won't skew it too much. If it's really printed off, I starch the fabric before cutting.
If you look at the quilts in the pictures section, you can see that most folks don't share this view. It produces a quilt pattern that's a bit less ridged.