I noticed LibBars a couple of days ago and clapped my little hands and roared with great fury: "Finally I'll get pretty bars!" Or.. Yeah. So, I don't know much about this new library - I'm going to assume it's the successor to Candybar? Anyway, I have some suggestions. Some may already be there, some probably aren't.
Borders: Can't live without them, they just make the bar look 'at home' - it blends in with the default UI.
Text: Enough options to change size, color, position, alignment of the text. If you can do it with Quartz you can do it with LibBars!
Bars: I believe Candybar was pretty much perfect when dealing with bar textures and its size and colors. Some addons screwed it up by only allowing 3 ugly colors, but that's another story :)