Hmm, can understand the swimmer situation, as he's not gaining any advantage by missing a leg. Well, unless the lack of water resistance down that side outweighs the kicking power, but even then, he's not gained from any artificial aids to the body.
Can fully understand Pistorius's desire to compete against the best, and i wouldnt have any problem with him competing in the Olympics if it can be proved that his artificial legs do not offer him competitive advantages. If they do, then they go against the whole ethos of the Olympics, which is for each athlete to show their natural ability in competition. If its shown his legs are designed to enhance and improve on his natural skill, then they cant be allowed. Otherwise we might aswell give Ben Johnson his gold back.
However, looking at his times so far, cant exactly see that being the case. Still its a dangerous ground ATM, on one hand you've got a persons desire to do what every athlete dreams of, in competiting against the best at the biggest stage on earth. On the other, you do have to consider that in a purely competitive situation only do those prostethic limbs offer an advantage over normal limbs (had to bold that part, because i feel like a bit of a **** arguing that having no legs is an advantage)