The Inquirer explains why the AMD Athlon 64 Revision F processors were delayed from the first to the second quarter of this year:
One thing we recently heard is that there was a fairly nasty bug in the DDR2 controller that made the chips pretty well 'blow' on memory performance.
AMD was not aware of this bug until fairly late in the game, and there was a new spin required to fix it.
Now, memory performance is said to be much better, basically to not blow. Updates on this level mean delays though, and that could be the reasons that the Fs went from March/April to June.