I'm supposed to get an appendectomy at the end of this week, and I read that a possible complication can be blocked bowel movements. Does this happen often in appendectomies?
This is called bowel obstruction from adhesions or hernia, every abdominal surgery has this risk.
Every type of intra-abdominal surgery has a risk of developing scar tissue that can cause a bowel obstruction in the future. Laparoscopic surgery, as I presume your appendectomy will be, has a much lower risk of that occurring. The risk of a future bowel obstruction is not so high that it should worry you or prevent you from getting a needed surgery.