I jailbroke my iPhone 3GS running iOS 5.1.1 three times in a row once.
Took less than a minute each time. The only reason I did it three times was because I didn't realize the first two times I had jailbroken it already. I was expecting a specific response from the program on the computer but not getting it - but the phone was still jailbroken. By the third time I finally figured that out.
Jailbreaking is far easier than it used to be.