Thanks for the link to the highlight reel. My impression of Jones is that he's primarily a speed guy. His acceleration through holes is tremendous, and he's very smooth. While he may not have elite top-end speed, he seems to accelerate to top speed as fast as anybody. You look at his runs, and he's pretty north-south with some ability to bounce laterally at speed; he doesn't have that dynamic lateral cutting stop/start ability like a Reggie Bush or Marshall Faulk. Even his long returns are pretty much straight up the field or rolling outside and just outrunning slower college kids. In the pros, he's going to have to bring a little more to the table. His speed and burst will make him valuable, but he's never going to see the kind of gigantic holes he saw in college. I suspect what he really needs to do is work really hard on his receiving skills and bulk up ten or fifteen pounds to be more effective taking on NFL tacklers.
If Jones can become a reliable receiver, he could add a dynamic presence to the offense. He clearly has downfield speed, and while he's a smallish back, he's bigger than most corners and faster than linebackers and safeties, so if he can really work on routes and catching the ball with his hands away from his body, he could be that matchup problem who gives defensive coordinators fits. This is the kind of player I expect to see getting fifty-plus catches a season as opposed to getting a lot of carries. I suspect we won't see the 60/40 carry split we saw with Barber and Julius Jones; more like 70/30 with Jones being worked in more as a third-down back, playing in the slot on other downs, etc.
The good news is that his work ethic is reportedly topnotch, and he obviously doesn't have an issue being a second banana, something that Mendenhall may not be as comfortable with.
Combined with the new TE, Marcelleus Bennett, another guy athletic enough to move outside some for favorable matchups, I wouldn't be surprised to see Jason Garrett crafting a more varied look to the offense, utlizing the size of Bennett and the speed of Jones situationally to put greater pressure on the defense. With Jones, a lot will depend on how quickly he develops as a receiving threat.