I was thinking about 'power' of HTML5. It can do new and fancy stuff, but older PCs will lag when attempting to render HTML5 heavy web pages! (Like this one).
Is it worth to write pages in HTML5 and step into Web 2.0? Or should I stay with HTML 4, which most PCs can handle? Should I go with "Design & Power" (HTML5) or "Speed" (HTML4)?
The difference between HTML 4 and HTML 5 is not binary.
If you use HTML 5 you don't have to use all of HTML 5, and you don't have to do things that require lots of CPU.