Signed packages?

[J.B. Nicholson-Owens]

First, Ubuntu looks like a fine system.  I'm also glad to read that the focus 
will be on catering to making things usable by novices.  It's quite a 
challenge, but it looks like Ubuntu is taking big steps in the right direction.

I was curious about signed packages.  Are crytographically signed DEBs possible?

If so, does Ubuntu use signed packages?  If not, is this something that is seen 
as a good idea for the future or unnecessary?

Any rationale to help explain how they're unnecessary would be appreciated if 
time allows.

Thanks.