Adding PPAs to software sources (in Karmic) is sooo easy:
You can either go to:
System>Admistration>Software Sources>Other Software>Add
and put in something like
(for example for thunderbird 3):
ppa:ubuntu-mozilla-daily/ppa
or
ppa:chromium-daily/ppa
Or you can use the cli tool add-apt-repository followed by the ppa.
Thanks Ricky of Digitizor.
