I'm learning to use TortoiseHG and want to pull from someone else's repository to see what a real, working one looks like -- how often they branch and merge, how much code they lump into each commit.
The amount of repositories must be quite large and I don't think there is a way to browse them.
There is a search function at
https://bitbucket.org/repo/all
that you might use to look for repositories about a certain topic.
The main page has a a few examples at the bottom (TortoiseHg among them). You might need to log out to see this list.
Finally, searching for Home site:bitbucket.org
in Google shows a large list of repositories and I imagine other such searches might be useful.