It's good to see new companies using Bitcoin, but I can't help but think this idea is a bit daft.
Rather than burning through energy and CPU/GPU cycles to earn a few quid, would it not just be better to ask for Bitcoin micro payments each month?
EDIT: To add, gamers are likely to have non-optimised rigs, compared with the next generation mining kit too, making it pretty wasteful. It is still good to see companies embracing Bitcoins though.
It would be better if gamers know what bitcoin is, how to use it and have them
But since almost no one know Bitcoin (let alone using it), the idea is nice.
The gamer just need to play and press "mine" and he will receive ingame bonus as time passes. That's all.
Then maybe hardcore gamers will discover bitcoin and pay for that in bitcoin, but it will be a later step