I am using the issue tracker to help facilitate communication with my client. It works great but as a non-techy type I have had to handhold him quite a bit.
There is probably quite a large subset of Bitbucket users who are "non-coders" - that is, they require access to issue trackers/wikis but don't really care about the code side of things, and don't have any idea what a repository is, etc.
What would be really nice is if those users could be given a streamlined user interface that brings issues/wikis to the fore, and puts the repo itself in the back seat (though probably a good idea to retain access if they want to take a look).
Also, I think the issue tracker documentation would benefit from a simple page explaining how to actually use the tracker - at the moment it's focused on adding milestones/components etc and assumes some prior knowledge of how an issue tracker works. Sure, it's not difficult but a page in the docs would save X number of devs explaining it to Y number of non-coders.
Thinking about it, even just a "Bitbucket for non-technical users" guide would be a great help - it could be a subset of the current docs and just walk people through what the different terms mean, what they will be interested in and what they don't need to worry about.
I know that non-coders are not exactly Bitbucket's target market, but making it easier for them would be very useful to people like myself and I'm sure many others.