In college I wrote a script to register for classes. I'd input the potentially-full classes I'd like to register for, and it would just hammer the registration site repeatedly until someone removed themselves from the class at which point I'd be registered. I'm still amazed IT didn't pull the network connection to my dorm room or have any kind of rate limiting. No 8am sessions for me!
Class registration was done by most with the web interface, but I opted to connect to the backing mainframe via a 3270 terminal emulator. Doing so allowed me to write a simple expect script passing in an increasing number as fast as the connection would allow. I didn't bother with rate limiting and am surprised nobody noticed. Took me about 30 minutes and I was in! I was able to use that script at least twice and I wished I had thought of writing it sooner.