There's an article on the main part of this site (not the discussion board) where Ian points out various flaws in Project Orion.
Having read it, I still think it's doable (and should have been done), but it might not be the be-all, end-all of space travel.
It's worth a read just to be sure you know about the pitfalls (EMP problems from firing the drive too close to Earth, for example).
However, to answer your main point, since Orion's drive gives it so much power, it would be very useful at getting big things places faster and could be useful for colonization efforts.
I read the book Project Orion and it describes how they could do a round-trip to Saturn in something the size of a WWII battleship in reasonable comfort (showers and the like).