I've used vudu on my ps3 this past month. No issues, and video quality has been really good. It's spendy for Hi-Def titles though - 5.99 or more.
I like it, but it's easy to rack up quite a charge as it's per movie.
Boxee is it's own delivery service - like roku from what I understand. You still need some other service to watch - hulu, vudu, etc. Unless you mean you're using boxee to watch vudu? It should work just fine, but you don't need boxee if you have a ps3.
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"There is an art to flying, or rather a knack. The knack lies in learning how to throw yourself at the ground and miss. Clearly, it is this second part, the missing, that provides the difficulties." - Hitchhiker's Guide to the Galaxy