I switched to Dvorak in 2001 out of curiosity, and because I was not very busy at work so I could afford the luxury of taking 20 minutes to write 1-sentence emails. I switched cold-turkey; one day I changed my keyboard layout and I didn't use qwerty every again except on other peoples' computers.
I would say that I hit a speed plateau after about 3 years. After that amount of time though, it's hard to say how much faster I am than I was on qwerty. The fact that I can't tell is a sign that it's not worth it. But I am pretty certain that, even if I'm not faster, I am just as fast.
And maybe more importantly, I do feel that typing is more efficient with Dvorak; I feel like I am more a part of the keyboard and that my typing is more fluid.
There are some other advantages to dvorak, like when company tries to use my computer, they get the strangest expression when they start typing. I don't tend to like other people using my computer, so this turns out to be a form of security.
But there are so many disadvantages --- everyone else's computer is on qwerty so you may struggle every time you have to go back to qwerty. The worst is if you have to use a customer's computer, and the customer sees you typing very clumsily they may lose confidence in your skills as a programmer.
Another disadvantage is that so many games and applications make assumptions about your keyboard layout so you will find that familiar WASD pattern scattered around your keyboard as a Dvorak user.
In the end, maybe the biggest advantage of Dvorak for me I think is just the experience. It's even psychological - it illustrated how I see words in patterns. Maybe I subconsciously type words in my head as I think them. Because when I started learning Dvorak, words started to "change shape" in my head and that was a bizarre feeling.