According to #mercurial, branches (even closed ones) begin to noticeably slow down the repository when you reach around 2000. That's not at all impossible to reach with fine-grained feature branches. Bookmarks are really just pointers to commits, no branches in any sense, so they cannot be used for feature branches either. As a result, we simply don't use feature branches in Mercurial. It's literally the only issue I can think of.
> We have users with thousands of named branches in production and have
> done tests on up to 10k branches and the performance impact is fairly
> minimal.
Well, if that true, I'd prefer to investigate and make them fast, instead of using "bookmark-as-a-branch" because of all the cool stuff mercurial branches have (like great log-drawing with branch info).
