But it's true-- apparently Blizzard felt that anyone drinking for only five seconds (either in a PvP or PvE situation) was getting too much mana. Drysc confirms that it's a serious change, and that anyone worried about their mana regen only needs to drink for six seconds, at which point they'll have as much mana as before the patch (which suggests that there is a burst of mana given at the 5 second mark, to make up for the delay).
But is this really that much of a problem? Sure, with the changes to spell haste, things are going to get faster in the battlegrounds. But are we at the point already where an extra second of out of combat drinking makes all the difference? Blizzard thinks so.