If it's not obvious from this blog, I feel equally committed between healing and DPS. And that means I have to think about respeccing. A lot. I have a paladin friend from another guild, who runs instances. A lot. All. The. Time. I'm on his friends list, and he often pings me to see if I want to heal an instance. Lately, I've had to tell him that I'm DPS right now, so I can't help. Really though, I could just respec. It's not as bad as it used to be. Having more gold helps, and having Spellpower gear (instead of +heal vs. +damage) help.
One of the annoyances is the sheer clicking to respec. I'm now using the addon Talented to solve that. It can save talent specs and automatically apply them, which is great. I use a slightly different option: I'll bookmark specs from Wowhead. Talented can parse the Wowhead URL and apply that spec to your toon. You can confirm that it's right before having it do all the clicking to spec you out.
A side note: if you're going to do this, make sure to click the "Link to this build" link in Wowhead. That will "lock in" your spec and URLify it. It's also the way to post URLs to specs. Otherwise you will get a blank spec — or worse, a look at the spec you started with instead of the one you wanted.
That takes care of most of the hassle. You still have to alter your action bars, replacing buttons with the new spells you've learned — or maybe just more appropriate spells for your spec. The bigger hassle in WotLK is to deal with your glyphs. The DPS glyphs are no use for healing, so you'll have to switch. This is the biggest cost; if you switch your 3 major glyphs, that might cost you ~100g for each switch. It's also annoying, because you'll have to get to the AH to buy glyphs, and then find a Lexicon of Power to make the change.
So: today, it's possible, mildly expensive and annoying just to respec, and more seriously expensive and annoying to switch glyphs. The good news is that this is going to change at some point. Blizzard is working on a dual-spec capability. The idea is exactly like what I would want: you can swap between two predefined specs, with much less cost and hassle. The spec swaps should also swap glyphs and action bars, and won't require you to reapply your "lost" spells when you switch. And you should be able to do it pretty easily and cheaply. To quote from an official Ghostcrawler post about spec swapping:
Of course this is subject to change, but if it stays in this form, life will be good. My A and B specs will be Resto and Balance of course, and I'll be able to move back and forth without too much trouble. Of course, for the most part the gear is the same which helps. There are a couple of gear pieces that swap +hit for MP5 or whatever, but as a druid, carrying around lots of spare gear is standard already.
Our thought at the moment is that swapping specs (going from A to B) will truly be free in towns and possibly during the prep phase of PvP. In an instance it may cost a nominal fee (think reagent level). We want you to be able to do it when you want to do it, but we also don't want to slow things down if everyone is constantly flipping spec from fight to fight. But if it's free in town, then obviously it can't be more of a burden out of town than just hearthing and being summoned back is or nobody will use the remote option.
It doesn't solve anything. You'll still have to pay (and re-glyph) if (for instance) you want to switch your B spec from Balance to Feral, or if you want to adjust to get more PvP talents. (You could choose to have your A-B specs be PvE and PvP of course.) Some people feel this is an unreasonable burden, but they won't be happy without on-the-fly free respecs. That too me sounds like overkill... because soon you'd be expected to respec at any time. "Oh, this boss does a stun, so everyone drop DPS spec points and put them into your stun resist talent."
That way lies madness. The A-B spec swap is the right way to go. And I can't wait!