I've been hearing more and more about CSS3 transitions lately. As a JQuery developer of a few years, I'm totally in love with how solid it is - robust animations that are simple to execute, and wonderful browser support. It's a very rare day that I find a requirement that JQuery can't handle.
Now, it's my understanding that CSS3 transitions have some bugs, and (by nature of being CSS3) limited browser support. It's also lot harder to time oncomplete and trigger events for animations you need to listen to. Some sites even provide a javascript fallback for their transitions/animations, and it seems pretty inefficient to me to have the same information in two places on a site.
From my perspective, there's no reason to stop using JQuery in favor of CSS3 transitions (at least not yet) - yet the practice is becoming more and more common, so there has to be a reason. Why do CSS3 transitions exist?