Some more impressions after another day of intensive use -- it's my primary system after all.

Frustrating problem -- Simple Solution
I was finding it especially frustrating trying to launch multiple instances of apps using the launcher or the super key. Thankfully, the super key comes to the rescue again. Holding shift-super-2, I can launch a new instance of my terminal (for example) on a desktop, without needing to go to the original instance and spawn a 'New Window' from its menu. I can also do this without touching the mouse, which is welcome at times.

Since I like to use shortcuts, this works for me, but for lay users or new users, use of the dock will be the only option and will certainly be frustrating to use at times.

I'm finding out that the best part of Unity is the fact that I don't have to use the key UI component, the launcher. Navigating and the super-key have made the experience bearable and in some ways quite a bit better than the original Gnome dock. The super-key launcher, IMO, is the single best innovation about this product, though it's likely to be accessible only to those that are comfortable using keyboard shortcuts.

Broken Search
Clicking the Ubuntu button, or hitting the super key on its own brings up an application/file search. This seems great until you realize how inconsistent it is to use. It works well for applications, but finding files is another matter entirely. Typing in a fragment of a known file on my system yield no results, or results only some of the time -- silly, right? What's worse? Directories are omitted altogether from the results. I don't know who coded this mess, but they need to be fired.

Suggestions for improvement
I would like to see a better way to quickly organize a bunch of on-screen windows. Blender handles this quite well with a user-defined pane system, and the new Touchwiz Galaxy Tab widget interface seems to have a novel approach to this as well. Currently, Unity incorporates the Windows 7 'snap-to-side', which is useful. However, the horrible top menu, and the fact that your window spills over onto the next desktop leads to some undesirable effects. I think it can be done far better.

I would also like a method to see what windows I actually have active on a desktop. Ugh. I would rather not have to do an alt-tab, or move windows around to discover what is running on a desktop at a given time. Again, the dock is at fault as this information should be available at a glance.

Tear down and rebuild the app/file search engine. It's that simple. This should be a simple search against an aggregation of keywords (possibly against a synonym database) collected from files and their contents (when available -- eg. ID3 MP3 tags). The code base should be *tiny* and very, very fast. The problem is that the search doesn't work, which hints at some poor fundamental design decisions.

Bugs, Bugs, Bugs
This version has some bugs, so you may wish to wait. On my system at present, the graphical performance of dragging windows around has degraded to the point where I'll be lucky to get 2fps, and some windows are failing to register mouse clicks. These are clearly bugs, and I have full faith that problems like these will be fixed in short time. In the interim, a restart is required...

At this stage of the game, developers should be conscious about what it takes to move around a few 2D windows. The UI out of the gate should be quick, smooth, and function more-or-less flawlessly. I can appreciate that there are some problems that need to be ironed out, but even on a fresh boot, the desktop is a little choppier than I would like, on a system that can certainly handle it.

Final Verdict
Let me preface this verdict by saying: this is my system, and I don't have the time or patience to try another -- I'm locked into the Ubuntu ecosystem. It would take something major for me to move to something else.

Unity is novel to the halls of stock Linux distros, though it leaves a lot to be desired, and is a rather poor implementation of something I didn't like to begin with. Strong keyboard shortcuts have helped balance the playing field, but I'm left longing for more.

I believe with some work, some of these concerns can be alleviated, though I'm left wanting some real innovation rather than misguided facsimiles of existing software. There's plenty of ways to improve usability and UIs, and I believe Ubuntu can do better.

But for the time being, if I were the type of user that wasn't tied to Ubuntu, I would either wait to upgrade (I did it because it was automated), or consider another flavour. There's more to hate than to love about Unity.