Unlike many other services, Vudu hasn't launched an app, but simply made their site iPad friendly.
We're sold on the awesomeness of Vudu. You get streaming HD videos with excellent quality - the closest thing to Blu-ray out there - and the price isn't too bad all things considered. We're also sold on watching movies and TV shows on portable devices like the iPad. Clearly some movies are better suited for the home theater, but it's nice to have some entertainment with you.
Vudu on the iPad is a bit less exciting. The primary advantage of Vudu over other services is the ability to watch those gorgeous HD movies, but the iPad version is like the PC version - it only streams in SD. Of course, the iPad isn't an HD device to begin with.
Still, if you've rented a movie at home and you want to watch it on the iPad, you can do it. It works the other way around too - you can rent a movie on your iPad and then watch it on the big screen. At the very least, it's an easier way to navigate than your TV remote.