If you merge between branches and HEAD in subversion, you most likely need to know at what revision the branch was created at. Assuming you don't have the luxury of the new merging features in subversion 1.5, here is a trick I learned from the svn docs.
svn log --stop-on-copy http://server/svn/myapp/branches/myapp-1.0
This will stop once it hits the revision the branch was created at, verses continuing on until r1. Previously I would log the entire branch, and do a grep for the comments I inserted when I created the branch. Not ideal but it worked. Now I use the --stop-on-copy option and I know real quick the revision the branch was created at. Giving me the revision I need to use in the merge.
svn merge -r 546:767 http://server/svn/myapp/trunk
Can't wait until we upgrade to subversion 1.5 or a DVCS.