So I've got the high-level concept of what the game is going to be about. The next thing to decide is which platforms I'll be developing for.
It probably goes without saying that Windows is immediately the first platform on the list. It's widespread, familiar, it's the platform I'm the most active on in terms of daily use and play, and there's no barrier to entry. (Releasing the Express editions of Visual Studio is probably one of the smartest moves Microsoft has ever made.) Depending on the specific technology used, you could also add Linux and Mac OS X, in theory, to this mix.
Mobile platforms are also an enticing option, since everyone and their dog has a smartphone these days, along with free time to squeeze in a session of gaming. It's not as simple as that, though. Your design must be able to work with the input mechanism present on the target platform. For an example of where this did not work, consider Quake III on the PlayStation 2. If you've never played that version of the game, consider yourself lucky. The control scheme did not translate very well to the PS2 controller, since it wasn't designed with that in mind (in actual fact, it sucked a pile of... well, yeah).
You can't just dumb down the interface across the board to support a more limited set of input signals, either. An example of this is the PC version of The Elder Scrolls IV: Oblivion, which, quite frankly, reeked of having been designed solely for a gamepad.
In my specific case, however, touch-based input, which is prevalent on the modern batch of smartphones, shouldn't necessarily be a problem, barring a few user interface alterations.
Chances are that any mobile version I release will be done for Android instead of iOS devices, for the simple reason that I can't afford to develop for Apple hardware.
Finally, we have the consoles. The PlayStation3 is out, right off the bat, since as far as I can tell, you need to be a licensed Sony developer to be able to release a game on the PSN, which probably won't happen real soon. Ditto for the Wii. The Xbox 360, on the other hand, is much more accessible, thanks to Microsoft's XNA Game Studio. The only catch with that is that South Africa is not a supported territory for creators releasing games with XNA... yet. Hopefully that will change once Live is launched locally later this year. If not, consoles will remain a closed door.
For the time being, I will be implementing the game using XNA, if for no other reason than it's swift to get a prototype up and running using it. If it ends up being insufficient for the full, released game, I can port it to SDL or another technology without too much effort.