I really like SourceTree, and it has comfortably taken the place of TortoiseHG for managing my HG repositories. For the first time I even trust a GUI to perform my commits, pushes and pulls (previously I insisted on doing this via command line).
The one feature I really feel is missing is the ability to filter the log view by branch. I know you can select "Current branch", to only show commits from the current branch, but I often need to see all commits made against other branches, and it's usually not convenient/possible to switch branch in order to do this.
It's the one feature I still go back to TortoiseHG for. Crack this and I'm all yours!