I have just discovered the wonders of proxy zealot rushing. I setup a pylon and 2-3 gateways somewhere near his base, spam zealots and attack. In silver league, this is effective about 70% of the time.
When I'm spotted and encounter heavy defenses, I can often switch to some other strategy with relative ease - since I control the access to my opponents base, I can usually fast expand and go air while he is blocked from his natural.
I'm not saying this is 100% victory - if he spots me early and/or manages a good defense, he can out-race me to the air - but still, it's usually quite effective. Besides the bordedom of repeating one strategy, what reason not to use this strategy all the time?
(Note - it is a bit less effective against Terran because they usually wall in quickly)