As an important note, please be aware that this is probably the worst thing I've ever written. I'm not removing it because people have discussed some important things in the comments. I am, however, working on a rewrite that is being slowed down by the holidays. You can keep reading this and writing comments, but please be aware that much of it needs revision, clarification, deletion and editing.
Being unable to access the PTR, I never really got to experiment with haste differences before the patch went live. Aware that I'm sitting pretty compared to a lot of other Restoration Druids at 610 haste, I knew I was still under the cap. I would have been a little better off if I could have gotten the chest from Heroic Faction Champions, but it only dropped once and I didn't win it.
So, Saturday, my little-PUG-who-can hopped into Icecrown Citadel 25 man. We one-shot Marrowgar, five-shot (I think) Lady Deathwhisper, one-shot the Gunship Battle, and then had to call it on Saurfang on account of having waaaaay too many ranged (we only had about five melee; made spreading out impossible). During this time I got to play around with both raid healing and tank healing, i.e. doing both in a fight, and I found, insanely enough...
My timing is off.
I'm down to just fractions of a second more than the one second cooldown, with 610 haste and Celestial Focus, and my rhythm was still disrupted. Not terribly, not so that I couldn't heal, not so that my healing suffered. It was just an annoyance, a tic; when I was hitting my buttons now was my internalized one second GCD, and I just wasn't there anymore.
Delleyentar asked me just yesterday if I was going to regem haste or go Celestial Focus. I'm convinced, however, that regemming haste is not the way to go. Besides being expensive, it's a serious blight upon your Spellpower numbers, which are the biggest boost to a Restoration Druid's healing.
To take Bellwether for example, she has 15 sockets. Out of those 15 sockets, 13 are straight 23 Spellpower gems, and two are 12 Spellpower, 12 Spirit (gaining three socket bonuses along the way; +9, +7 and +5 Spellpower) . That's 347 Spellpower, including the amount gained from the Spirit. At 610 haste, I would need to regem 246 Haste to reach the fully-raid-buffed cap without Celestial Focus, which is 12 sockets of pure Haste and one socket of Haste/Spellpower. Fully regemming would get me to 910 Haste, but I would lose all that Spellpower and Spirit for a few seconds shaved off my GCD.
It's not worth it.
It's not worth it at any level; when you're low haste or high. Unless you're just a few points shy of the 1 second GCD, you're losing more by going for Haste gems. Spellpower is still priority. I'm going to be re-tweaking my Gemming Guide to explain this in detail, but I thought this deserved its own section, as well.
The one second GCD is not the be-all-end-all of Druid healing. Is it handy? Yes. Is it necessary? No. Can you raid heal without it? Yes. Is respec'ing into Celestial Focus helpful? Most definitely.
Don't gimp yourself trying to reach the one second GCD. You won't perish without it, and neither will your raid.