If you are an screencaster, for sure you know that there are not much options to grab your desktop + microphone at the same time. Perhaps you have tried some java programs, or simply switched back to windows and used a virtual machine. Too complicated!

Hopefully, there is still an opportunity: recordmydesktop+jack. I will not describe how to install jack here, sorry, google is your friend :)
But once you have jack up & running, do the following:

Download sources
$ apt-get source recordmydesktop

Install development dependencies
$ sudo apt-get build-dep

Configure and build package
$ cd recordmydesktop-0.3.8.1
$ ./configure --prefix=/usr --enable-jack=yes LIBS=-ljack CFLAGS=-DHAVE_LIBJACK
$ fakeroot debian/rules binary

Install your own recordmydesktop with jack support enabled
$ sudo dpkg -i ../recordmydesktop_0.3.8.1-0ubuntu1_i386.deb

Now, after 10 minutes of copy paste, you ubuntu box is ready to use gtk-recordmydesktop + jack :D

Blessings.