I don't think I'd ever buy one, but they're certainly fun to use and might be worth renting now and again for a shoot. Last time I used one it worked well for me as it was for an interview where the guy was doing a lot of forward and back head movements, which would have made it a pain if I had to constantly pull focus with a traditional lens. With the TS I was able to put him in a vertical plane where he could move forward and back as much as he wanted and would still be crispy. In my opinion it has it's uses outside of what it's 'meant' for, but I'll probably just stick to renting them when needed.
The Main Idea