I've been trying out Viscosity for a while and I'm rather pleased with it so far. Just one, tiny thing though, I'm using the Transparent World menu bar icon set, and there's no icon for the highlighted state! I've made one real quick to show you what I'm talking about:
I haven't checked the other icon sets, but I hope you'll implement the highlight in those that need it as it looks much better. Sorry if I'm being too much of a perfectionist.