We've release Mockups 2.0 at Balsamiq. The main feature in this release is the Symbols functionality. It allows you to reuse groups of controls in order to create templates, page masters, and libraries of re-usable components. This can be done globally for all of your projects, or locally within a single project. You can create symbols from the top down and the bottom up. There's some documentation for this somewhat advanced feature here: Working with Symbols. To try it out, download or update Mockups on your machine.
30 Nov 2010