My sister went to a TGI in Coral Springs, FL years ago. She paid for her meal by credit card and left the tip in cash. When I do that, I usually write the word "cash" in the tip line. She was still in high school so she was naive and left the line blank. The server went ahead and put $20 in the tip line (if I remember correctly...it was an incredibly large amount though). Her bill had only come to $10. That's a hell of a tip. When my parents got the credit card statement (my sister used their credit card), my parents were livid. They called the restaurant manager. The server was fired and my sister was given $50 in gift certificates. At least they took care of the problem but it still says a lot about the type of people the company hires.
I've never been impressed with the service when I've dined there unless I was seated at a table where I knew the server. This happened frequently when I was back in college. My server friends would "forget" to include some of our drinks or appetizers on the bill.
I haven't been to a TGI in years. There isn't one by my house and the food isn't good enough that I'm willing to make the drive.