Over at The Supreme Court Nomination Blog, Kevin Russell, Anisha Dasgupta and Brian Fletcher have looked at John Roberts' complete voting record on the DC Circuit, and conclude that it didn't show any particular ideological patterns:

While Judge Roberts agreed most often with some of the court's most conservative members (agreeing nearly 100% of the time with judges Ginsburg and Silberman), he agreed nearly as often with some of its most liberal members (agreeing 95% of the time with judges Rogers and Garland). The two judges with whom he disagreed the most were relatively liberal judge Edwards (disagreeing in whole or part 18% of the time) and quite conservative senior judge Williams (10%).

  Of course, as they note, it's hard to read too much into this: Roberts has been on the DC Circuit for only a brief time, and a very high percentage of DC Circuit opinions are unanimous.