Nowadays people usually prefer a 64-bit system. It's as stable as Ubuntu 32-bit.
However, Canonical only sells the 32-bit variant in the Canonical shop.

I'd like to buy an original Ubuntu CD in 64-bit.

I love and appreciate Ubuntu's leadership in the Linux community, however I am ultra-hungry for solutions that help Ubuntu deliver real Knock-out punches for market share; so in this spirit here is some food for thought which I hope reaches the right people.

I'd like to share how the decision of replacing XP machines in two years is being processed where I work:

1- Ubuntu Server has made inroads into our company and is well appreciated.

2- Windows is still the 98% deployed OS and Ubuntu Desktop is gaining popularity only among tech people.

3- I am the IT Manager and recently made an evaluation of switching our XPs to Ubuntu.

4- I determined that in-house software could always be re-oriented to run on Ubuntu clients, but it would take energetic selling to peers and execs.

5- I hit a wall when I realized that existing 3rd-party solutions would not be able to run on Ubuntu:

a) Call-center Client Apps
b) IE-dependent Web-based Apps
c) MS-Outlook-dependent Apps

Additionally, The absence of a real-world replacement for MS-Outlook to access MS-Exchange and other servers is notable in the Linux community.

Although this is not a complete analysis, it clearly points to some of the main reasons why Ubuntu is being held back as an enterprise desktop.