Currently I am following F13 and I have been noticing a lot of packages disappearing from updates-testing before showing up in the branched release (but similar things happen with normal updates, just less often).
When things disappear from updates-testing it isn't immediately obvious if this is because the updates are bad or because the update has been pushed to stable.
Since I have a local mirror and the packages disappear between syncs, I end up downloading them twice. When stuff ends up having the same key regardless of testing status, this is especially wasteful.
What I'd like to see is stuff stay in updates-testing for a while so that the hard link feature of rsync can be used to avoid downloading the data twice. And so that I don't get false alarms for stuff that may need to get downgraded.