Bryan, It's really up to the browsers to do what the standard says to do. I don't think any browsers are ready yet for the spec and again the spec isn't even finished. For example I don't think any will honor border-radius yet, but WebKit based browsers support -webkit-border-radius and Mozilla based browsers support -moz-border-radius.

I'm with you on wanting to use css3 now, but we're still going to have to wait for browsers to adopt it. For now we'll have to use progressive enhancements for some browsers. By the way you can use JavaScript to created rounded borders. I've used jQuery for it in the past. Maybe I'll see about writing a post on how.