I'd be happy with this if the default was mtn pull <default_host>
<current-branch>, but the current setup which has the pull use the
first branch ever pulled doesn't work well if you're working on
multiple projects. I also wouldn't want it to do a mtn update unless
there are currently no differences because it's much cleaner to do
merges between committed revisions than with an existing workspace,
and it's also possible to undo mistakes if it's committed and harder
if it's not.
The reason I would want the pull based on the current branch is as
follows. In the setup we have at work, we have a central server that
has all the branches anyone wants to make public. Most people only
keep a single personal database of all of their monotone work, and so
their database will have a subset of the branches on the central
machine. They don't want everything, so pull of all branches would be
bad, similarly their current directory may be a branch that wasn't the
original branch they pulled so that would also be wrong.