1. No plug-ins required – it can only use features natively supported by the client
2. Compatibility – it has to work on every major browser on the market
3. Ease of use – no or near-zero configuration needed for standard use cases
4. Speed – it has to be fast, even for sufficiently large amounts of text
Cufon: Fast text replacement with canvas and VML – no Flash or images required.
(via twittering jason santa maria)