In my existing (Pre-SVN 1.5) merge strategy, we create a copy of the Trunk (called BasePoint) at the moment of branch-creation for referencing later during the merge.
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I believe reintegrate does not actually do the two operations, but instead is used to merge back into trunk from an updated branch. You will still need to do the first set of merge/commit operations to update the branch first.
Here is a link to the Subversion Book. It is possible to get this book in dead tree format.
From the link, it sounds like using --reintegrate handles some weird cases, probably like merge usually does compared to just using straight patches (read the section "Why Not Use Patches Instead?").