I just installed this plugin, and I have to say it looks great! I love that it's entirely made with CSS and fonts (no raster graphics), which I can easily customise further using CSS.
I'd like to offer a couple of ideas or requests though, to make it even better:
1) I'd love to be able to add alt-text and title to each button (on a per-button basis) - the title could provide the useful browser tooltip with eg. "Like us on Facebook" etc.
2) I'd love to be able to change the button order.
3) I'd love to be able to select which ones open in a new window and which ones don't.