also important to note: each stylesheet cannot have more than 4095 CSS rules, in IE. experiencing this limit makes for some mighty interesting debugging.
It's not that unreasonable. Scenario: You download the Fugue icon set (http://www.pinvoke.com/). You're working on a template, and want to be able to quickly try out different icons in different places. If you generate two rules for each of the 2500 icons, you're over the limit.