Pardon my general n00bishness, but I crave knowledge. IIUC currently if you have a checkin in trunk that you *don't* want merged into py3k, you must svnmerge block it in py3k. Otherwise it will be automatically merged at some point.
My question is: when will we stop doing that?
Nobody has really answered this question, so let me try: After 2.7 is released (i.e. within two months), the 2.x branch (i.e. the trunk) will be closed for changes altogether. So merging changes from trunk to the 3.x branch becomes unnecessary, and we can stop doing that (*).
Around the same time, we will also switch to Mercurial, so the point of using svnmerge and blocking changes becomes irrelevant for that reason, also.
So in short: in less than two months.
(*) there still might be bug fixes applied to the 2.7 maintenance branch which also apply to the 3.x branch. I would expect that there won't be an automatic migration of all changes in either direction, and that, with Mercurial, migration of selected changes can occur in either direction. In any case, this will not be about the trunk.