No and I would strictly discourage from it. There are so many possible side effects that you will encouter with an automatic merging.
How would you resolve conflicts? The more development means more changes in branch and trunk, means more conflicts at merging. The merge must be done by hand.
What about unwanted merges? There are things (like changing version numbers, dependencies, etc.) you don't want to merge back. With an automatic merge you had to reverse merge the merges, wich causes more confusion and work.
With the merge tracking feature of SVN 1.5 you'll get good information and see if someone hasn't merged his/her changes back to trunk. You just have to use it properly.
