What is Utnubu?

Not Ubuntu,I heard it on Planet Ubuntu but google doesn't tell me anything.

It is something related to Debian.

Utnubu - Ubuntu spelled backwards - is an effort to package Ubuntu-specific packages for Debian. While historically most applications have been packaged by Debian developers and imported into Ubuntu, there are a growing number of applications that have been packaged directly by Ubuntu developers and which could easily be imported into Debian.

You can find out more on the Debian wiki page. There is also a mailing list, and, as maco pointed out, an IRC channel.

Do you mean this?

One of Ubuntu's activities is frequently redistributing packages originally from Debian to Ubuntu's users. Well, Utnubu is about the reverse, copying packages from Ubuntu to Debian.

I've never heard of this before. I assume it's real. =)

It's the effort to work together with Debian. Check out the #debian-ubuntu channel on OFTC