I think you may be asking what the defferences are from one's perspective?
I personally have used both and didn't notice any difference in usability perhaps that Ubuntu is a straight forward install?
You raised a good question and I found an interesting read at least I think so, so am sure you have read it before, its on the Ubuntu site:

Differences between Debian and Ubuntu:

http://www.ubuntu.com/ubuntu/relationship
  
 On Saturday, February 10, 2007 10:29 AM, Pete Daniels wrote:

Date: Sat, 10 Feb 2007 10:29:12 -0600
From: Pete Daniels
To: TCLUG 
Subject: [tclug-list] N00b seeks advice; Ubuntu vs. Debian

  As I've said in this space before, I've been an Ubuntu user for the entire <2 years I've been using Linux, and it's been reasonably good to me.  However, in light of some recent decisions made by the Ubuntu camp (the "binary video drivers by default" announcement re: 7.04 in particular), and simply in the name of broadening my horizons, I've made the decision to strike out for greener pastures, and am planning on installing Debian Etch when it finally ships.  So, my question is this: Could anyone out there help me out on some of the differences I can expect to encounter?  Sorry if this is an overly broad question, I really have no specific "thing" here... 

best!
-p.
   
"Great Spirits Have Always Encountered Violent Opposition From Mediocre Minds" - Einstein

"Cuanta estupidez en tan poco cerebro!"
On Saturday, February 10, 2007 10:29 AM, Pete Daniels wrote:
>
>Date: Sat, 10 Feb 2007 10:29:12 -0600
>From: Pete Daniels
>To: TCLUG <tclug-list at mn-linux.org>
>Subject: [tclug-list] N00b seeks advice; Ubuntu vs. Debian
>
>As I've said in this space before, I've been an Ubuntu user for the entire
><2 years I've been using Linux, and it's been reasonably good to me.
>However, in light of some recent decisions made by the Ubuntu camp (the
>"binary video drivers by default" announcement re: 7.04 in particular), and
>simply in the name of broadening my horizons, I've made the decision to
>strike out for greener pastures, and am planning on installing Debian Etch
>when it finally ships.  So, my question is this: Could anyone out there help
>me out on some of the differences I can expect to encounter?  Sorry if this
>is an overly broad question, I really have no specific "thing" here...
>
>best!
>-p.
>

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