Comment 7 for bug 603574

I don't have any preference. I think since ligatures are missing (or not "true" ligature in the sense that a ligature should be a different glyph) from the Ubuntu Font Family itself, you're going to get these warnings.
I'm going to have a look to texlive-fonts-extra package to see what they provides.

Since the font family misses a "fixed teletype" font, I think it's a bit prematurate to create a special package, or to integrate it in texlive-fonts-extra.