Bar Dupont certainly has its moments. If you can hit it up when it's quiet (after happy hour on a Tues or Wed), the vibe is very cool. The views through the giant glass windows of Dupont Circle are fascinating. The relaxing furniture helps for optimally soaking in those views.
The downside is that it's usually too loud to have a quiet conversation as a result of the way sound travels and the techno can get to be a bit too much- take your first dates somewhere else!
Pros: Comfortable lounge seats and awesome view
Cons: poor acoustics and imposing music