I've been using Ubuntu for a very long time. I was one of the few in the media who adopted Unity as my primary desktop interface. In fact, I've grown so used to Unity that I have trouble finding any form of efficiency in other desktops. So, naturally, when a new Ubuntu release is about to be unleashed upon the world, I grab a beta and install it.
The hype surrounding the upcoming 13.10 (Saucy Salamander) was fairly significant. Leading this charge was the much-anticipated switch to Xmir. Well, thanks to a few show-stopping issues (such as dual-monitor support), Xmir has been pushed back to 14.04. Is this a big deal? Yes and no. Yes, because Xmir will be a major change to the sub-systems of Ubuntu. No, because Xmir must be faultless when released -- otherwise, the backlash will knock Canonical back so far in the past that they'll have a hard time recovering in the eyes of the Linux community.
Beyond Xmir, the biggest change from .04 to .10 is the much-maligned inclusion of Smart Scopes. What are Smart Scopes? Let me explain it in the simplest terms as possible.
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Also: Ubuntu 13.10 in-depth video review