Hi!
Domas' concerns about hardware support are also illuminating ([1]). Has the switch to MySQL-5.1 alleviated those at all?
The switch hasn't improved anything (oh well, except crash recovery, and we used that feature already once! ;-) - maybe made developers a bit happier that they will be able to write less efficient queries in future.
We did defragment our databases during the switch, so diskspace concerns are not that big anymore. Still, we need new hardware, and as long as it is procured and deployed, we'd be safe deploying FR.
Domas