[germanforblack]

Performance of long CSS files isn't really the (major) concern —its how many _elements_ are being traversed (size of the dom) that really effects CSS-selector performance.

[ricardobeat]

After a certain point the number of selectors does affect parsing time and selector matching time, in a very significant way.

Performance has improved a bit since this post but it's still relevant: http://perfectionkills.com/profiling-css-for-fun-and-profit-...