I've seen that some Google Webfonts now use WOFF 2.0. Can I somehow convert my existing WOFF-fonts to this new (and supposedly better format)? And how?
Certainly! You can convert the existing woff files to the new format. You will get more than 30% improvement on the compression ratio.
Even though browser support is limited at this moment
http://caniuse.com/#feat=woff2
It will eventually change. You should use the @font-face fall back and start putting these kind of directives in your css now.
@font-face {
font-family: MyFont;
src:
url('font.woff2') format('woff2'),
url('font.woff') format('woff');
}
You can use the following tools to convert from ttf/woff to woff2.0