You will likely get more informed responses from the RIP owners out there but what I usually tell people is that:

(1) QU doesn't replace the driver.  It uses it and works with it.  Think of QU as software that optimizes data for the existing Windows driver.  So it is not a RIP.

(2) Having said that, it does perform a lot of the functions of a RIP and some, it does even better.

(3) The one thing that QU cannot do that RIPs do is that it cannot provide the specialized black and white functions of a RIP.  That is, some RIPs offer functionality that prints without using certain metamerizing inks like yellow in order to give you more neutral black and white prints.  So I would say the one area where QU cannot match a RIP is B/W printing.  Now, whether or not you need that level of B/W functionality depends on how often you print B/W, what type of printer, ink, and paper you are using, what type of light source under which the prints will be viewed, and a few other factors.  It's probably safe to say, if you don't know what I'm talking about, you probably don't need that functionality.  

(4) Since QU works with the standard Windows driver, it can support nearly all printer models.  RIPs usually only work with anywhere from a few to a few dozen models, and you may or may not find your particular model on the list for which any given RIP supports.

Regards,
Mike

Hi Scot.
Since most Qimage users strive for the best color reproduction and the finest print detail possible, many of us use a proper printer profile which matches our printer, paper choice, and ink.
Once this is set up in Qimage, you accompany this with turning off the Color Management altogether in the printer driver.
Now Qimage Ultimate will use the best interpolator coupled with the profile, to make a print file that goes through your driver maintaining its integrity.

Nice folks on here. You will always find friendly and courteous help.

Fred