Check out http://www.modernizr.com http://www.modernizr.com, for example, which abstracts feature detection for many advanced "HTML5" features. You (sorta) don'

Check out http://www.modernizr.com http://www.modernizr.com, for example, which abstracts feature detection for many advanced "HTML5" features. You (sorta) don't have to worry about browser version, you just have to worry about feature support. Feature detection is a far easier strategy for development than user agent sniffing, in my opinion at least. Granted it's less helpful for CSS-related issues, which more have to do with inconsistent implementation than with whether a feature is or is not supported.