I use a head-tracking mouse and some old dwellclicking software (from the old smartNAV) to operate my mouse hands-free on the computer. I'm a quadriplegic who can't use his hands. But the mouse thing isn't close to optimal for any type of fast-twitch gaming, so I have largely relegated myself to civilization building or 4x types of games. But I also recently started playing Eve Online again (sci-fi with some space combat), and VoiceAttack has really been helpful. I only downloaded it a couple of weeks ago but I see the potential and I have already used it to increase my efficiency and ease of use in the game by quite a bit. I'm pretty happy with it and I could see using it in many other games.
I don't know enough about what's required for mouse control in typical quick-twitch FPS games but I can really see using VoiceAttack in a lot of different games in a lot of different ways.
I'm pretty glad to have it. My hands-free mouse situation isn't as good as it was back when SmartNAV was still being made.