How long does it take you to design a game? I am not talking about to levels of perfection but from first spark of an idea to something that is workable and playable.

Also where do you do your best ideas thinking?

Knowing that the OMG contest was approaching, I spent some time thinking about what to do for an entry. Once the initial idea had popped into my head it took me about an hour to finalise all the details in my mind. I've yet to put the ideas into a design document but that will not take more than 30 minutes or so.

The thinking for this design was done in the very relaxing surroundings of a Greek Herbal Sauna and a couple of meditation rooms. Usually I do my best thinking for games in the sauna at my local gym.

Really depends on the game. A lot of indie games just take some pre-existing game and either clone it or add a couple new features- a few games I have done in the past I haven't thought about the design until I implemented the base clone, and then a lot of the design was just working out the nuts and bolts (for example, you might think there's not too much to a breakout clone, but you have to consider how fast you want the ball to go, what happens when the ball hits different parts of the paddle, what happens when the ball hits the paddle horizontally instead of vertically, sizes of bricks, etc...)- though you might consider the 'parameters' of the game similar to what you would do in level design, since the game could be workable and playable before it works and plays well.

I agree... Depends on the game. I said years cause I hate shitty noob 1 day games. Too bad we don't have a firing squad... for things... like that.

From idea to a prototype design, it usually takes me on the order of hours. For OMG, I had a few designs in my head and in notebooks, and it actually took me longer (a few days) to choose one from the bunch. The idea I ended up choosing was also a design that I hammered out in a few hours.

Any idea that I've had in my head for years is there because it's either so ambitious that I'll never have the resources to do it (a sprawling RPG or super-stylish cinematic 3d game) or because it just plain sucks. Most often it's both.

I typically do my best thinking in the car, or daydreaming in classes. I go to a gym, too- but I never thought of the sauna. I'll have to try it.

A few days of off-and-on thinking for me. I don't have much time to work on my own projects so for contests like these, I usually go for something simple and not too complex. It doesn't help that the day job already consists of game programming.

If it's for a contest, I could design a game quickly. For many of my games, though, I do much design in my head, weighing options when I have a little free time (at the gym, driving in my car, taking a break from studying). Only after a month or more of thinking about the game am I ready to pursue it as a real project - much different from my old days of "Who needs a good design, let's code!"
Part of my long design time is that I have many other projects going and I just keep in mind "the next big thing" that I want to do. Right now I'm having a difficult time choosing between three different coding projects I could take on, one being OMG Cup...

I'd like to know who the four people who voted "years" are, and what it is that takes them so long.

I could have said years. I would assume they meant from conception of the idea to actually beginning development, and not years of constant work developing the plan. I think we all have a game or two, like Justin said, that is just too big for our resources, but that we've had in our brain for years. Would you count that über-game as being in the design stage for years if someday it is finally realized?

I was meaning from idea to start coding on the projects you have done so far.

I did answer years. This is because I tend to keep ideas rattling around in my head forever before actually sitting down and start working. The game I'm planning has been in constant thought progress for 4-5 years.

<note: I'm talking about arcade games, (the only ones I do)>

once I have a concrete idea and start working on it, I can make a playable prototype in a few days.

To have an idea good enough to get me coding can take months.

>I was meaning from idea to start coding on the projects you have done so far.

If the idea is interesting enough by itself, I start doing it immediately, to see what it looks like (like in a demo), then I release it shareware even though it's lacking everything that constitutes a game, get bad reviews and start improving :-)

Once I start thinking about a game idea I normally start to code it out. I know that is a bad habit but I work through Ideas better in code then I do on paper.

Just like Fenris said, I keep ideas fermenting inside my head for years before even attempting to start to implement anything. As I am no professional game developer I am in no hurry to develop a game. Still I like to keep my ideas organized inside a design document or even inside a potential design proposal before that.

You never know when you might have the chance to show your work to a potential team/team member and what better and simple way than keeping it all written down.

Estimated:
Antack: 90 days
Dead Days: 8 days
Dawn of the Derby: 15 days
iGame3D 4 freakin years
Next Game: 180 days

Ya know. I really don't know how long I take to design games...
I've got one game in my head that I've been meaning to program for about a year.
The game I'm currently working on I thought of about a week ago and started coding it the next day... So, either years or days :-P