Excommunication from the mainline, apostate, Presbyterian Church USA denomination? Almost never.
Church discipline, or disfellowship (which is what excommunication is) from the smaller, biblically faithful Presbyterian denominations, like the Presbyterian Church in America, the Evangelical Presbyterian Church, or the Orthodox Presbyterian Church? Happens not infrequently...when a member (or more typically a leader) refuses to repent from some sinful activity. Real churches still exercise the discipline commanded by Jesus Himself, in Matthew 18:15-17:
If your brother sins, go and show him his fault in private; if he listens to you, you have won your brother. But if he does not listen to you, take one or two more with you, so that "BY THE MOUTH OF TWO OR THREE WITNESSES EVERY FACT MAY BE CONFIRMED." If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector.
It is quite true that few even evangelical, bible-believing churches have the guts to follow this command adequately. Out of fear for being called "intolerant," or worse still, lawsuits--many pastors forego obeying Jesus in this.
Some churches now even, in their membership, require a signed statement that formally acquiesces to such discipline, if needed--just to try to avoid the courts allowing suits coming in and wiping out the assets of a congregation.
Welcome to 21st Century American liberty...