We do not 'evolve' as such anymore. Someone with a severe health disorder is very likely to survive nowadays (Albeit in poor conditions; I don't mean to take away from the people suffering), and, as such, the genes are often passed down. On the other side of the coin, having an advancement (Strong heart, better eyesight, etc) presents no real "advantage" on the reproduction field, as we do not need to defend against predators or scavenge for food.
That said, I suppose in a really remote tribal colony evolution could well take place.
Some, however, consider technological advancements to be our new 'evolution'. In this case, there is little limiting our advancement. The Laws of Physics are our only barrier, and god knows how stable even those are.