We do an enormous amount of wireframing using Balsamiq. It is a fantastic product and resolved some very basic issues we faced during the UI phase. Namely, since using Balsamiq, we no longer have to constantly dodge the design discussion during wireframing. Perhaps it is the artful mix of comic sans and crooked lines.
The app is in a constant state of improvement and as active users, we have requests. If you happen to use Balsamiq and want to weight in, vote up our requests:
Shortcut Key to quick add + add item where my mouse is.
Check out our WordPresss admin patterns for some examples of balsamiq in action.