Looks like Jason Carreira has stepped up to the plate to try and consolidate the validation frameworks we have in Java. I'm sure it was a joint effort among many, but Jason's name is the only one I see on the JSR. I applaud this effort - it's definitely needed.
I've used Commons Validator, the XWork Validation Framework as well as Hibernate's Validator. While Commons and XWork work, the ability to annotate a class and validate it anywhere/anyhow is pretty cool. I reviewed an article a couple months ago that hooked Hibernate Validator into Spring MVC and Prototype for client-side validation. There's a lot of good stuff in this space - let's hope this JSR creates something even better. More than anything, let's hope it doesn't brush off client-side validation like JSF did.
In an ideal world, the RIFE, Spring MVC, Stripes, Struts, Tapestry and Wicket developers will all participate and allow JSR-303's result to be used as their framework's validation engine. I think it's a given that this will be usable with JSF.