[CCJester]

As a "more often than not" protoss player, who uses blink regularly against lower league zergs, i have to agree with the posts before me. Scouting is your biggest defense here. Sacking an overlord at 6.30 - 7 and scouting the front to see the sentry count are big tools to not only see whether blink is a factor but also what sort of push it is.
I would perhaps suggest in a heavy ling / roach response, cutting a roach or two and trying to push for an early +2 attack on those lings but that has been something i have been playing with when i roll random and i'm not too sure yet on the full repercussions of infestor timings if you do this.