A few things...
First of all. you mentioned that Ubuntu is the unstable branch of Debian, not entirely true. Edgy, the latest current release is to a large extent the testing branch of Debian, effectively half between unstable and stable.
The version just below Edgy, Breezy is the LTS, or long term support. in other words the one aimed largely at business users and those who want the most stable version of Ubuntu thats not obsolete.
Also, I noticed Linspire, I did review a couple of the latest version about year ago for a computer site, I have to say whilst it does some advantages, it has more disadvantages, in particular, the software it came was *really* out of date, and not particuarly stable.
Also it should be noted, the linux x-server (the core of the graphics basically) is distincly slower than that of Windows.
Apart from that, I really like Ubuntu, and see the post I am replying for more of the good points. They are plenty. BTW, Ubuntu and debian make it really easy to get and install software.