The CSS3 Specifications are in the main browsers partly implemented and you get very nice results with less code, but there are many reasons not to use CSS3. E.g. not downwardly compatible, probably not similar renderd views on different browsers, etc.
So I’m asking myself: Which is the best way to use CSS3 anyway with a option to intercept default problems, like I’ve discribed above?
As long as your site degrades gracefully there’s nothing wrong with using CSS3 now. Afterall, if a browser does not understand a particular CSS rule it will just ignore it:
As long as the site does not look broken in browsers that don’t support the CSS3 rules you want to use then you should be ok progressively enhancing your site in the browsers that do support them.