The Atlassian way of handling sub issues is to only calculate their workload using time estimates. This is not how all teams work, and it would be nice to have an option on the board that lets you set if sub issues should be treated just like any other issue. This would broaden up the use of the rapid board for more of its users.
One problem with the current implementation is that story points on sub issues are not shown in the burndown chart. Any subissue is not shown in these charts at all. This makes statistics gathering somewhat hard to do if you treat issues in this way.
An added bonus would be if the combined value of the story points could be viewed on the parent issue as a calculated field. This calculated fields should not count towards the statistics of course.