Looks like Blizzard is going to change the way drink regen mana with 2.4 to accommodate the hard-core arena guys. In a nutshell, drinking will now be on an improving timer, so those quick 10 seconds drinks to cap off mana before another pull in an instance won't be possible any more.
This is a stupid change to make to a major game mechanic for the 10% of players who are that hard core. I hope Blizzard sees the light on this before they make 2.4 public.