Design looks different in different browsers. If a large percentage of your traffic uses IE, this is probably not good. If your CEO does a little browsing on IE and doesn’t understand what happened to the design, this is probably not good.
If your traffic/user base justifies a pure CSS3 approach, I say use it. The advantages are real and it’s the future of web design.
However, if you’re forced to do the CSS3 with fallback to images approach, I would probably avoid using CSS3 altogether (especially if the site is large or complex).
I started out doing a project the hybrid way and ended up scrapping it for background images for all browsers—I didn’t see the advantages as outweighing the development costs. Plus, the markup would be handed off to a different team for implementation and maintenance, which means that team would need to know to change the CSS3 in one place and update the background images in another.
Browser Version OS Results Chrome 5.0 Mac 43/43/0/0 Firefox 3.0 Win XP 43/36/0/7 Firefox 3.6 Mac 43/43/0/0 IE 6.0 Win XP 43/10/1/32 IE 7.0 Win Vista 43/13/4/26 IE 8.0 Win 7 43/22/1/20 IE 9 preview Win 7 43/43/0/0 Opera 10.52 Mac 43/43/0/0 Safari 4.0 Mac 43/43/0/0
From my understanding, v3 isn't a direct replacement for v2 but instead is a complete re-write from scratch. V3 on the other hand, being a complete re-write, has very few features at this point but is extremely efficient, fast loading, modular and potentially much more extensible.
I would recommend that any developer who is considering using v3 think of it as a "mobile only" API
We wanted to get this in your hands as soon as possible, so we've intentionally released it early, and with a basic set of features. We're releasing it in Labs because it's not fully baked yet; we want to get your feedback on the new design and what you'd like to see in future revisions now that we have a chance for a fresh start.
I would urge you to not think of this as a "mobile only" API. While mobile browsers are a new focus for us, the API is fully supported on desktop browsers (including the addition of Chrome).