After using Ubuntu 11.04 and Unity for the past few days, I'm actually enjoying it. Being used to the Gnome and Windows-style window management, I expected the worst, but it's not too bad, especially the new Launcher and effective use of screen space. It's kind of clunky right now and isn't easily configured without the CompizConfig Settings Manager, but I think it has serious potential.
Not everyone will like it, but it's definitely worth trying out.
By the way, you can stop the Launcher from auto-hiding by opening the CompizConfig Settings Manager (not included by default), going to Desktop > Ubuntu Unity Plugin and changing the Hide Launcher box to 'Never'.
However, after using regular E/Gnome/KDE/OS X/Windows for so long I feel handicapped with it; for example I can't right click on Unity bar to customise it and it doesn't seem to behave as I expect it to. I guess part of this is because of learned behaviours over the years and I've gotten used to UI's working in certain ways.
I'm not willing to rule Unity out, yet. But, I'm not going to upgrade my main Ubuntu system to 11.04 unless I can be guaranteed I can move to regular Gnome and back to Unity without problems. At the moment, I believe that, Ubuntu 11.04 only supports Unity and the Gnome 3 packages are in a PPA (Personal Package Archive) that isn't fully supported, yet, and might be quiet buggy.
I've also been thinking about going back to using Debian as I'm finding some of the ease that Ubuntu is bringing to Linux is at odds to a long-time *nix user like myself.
I gave it a fair shake initially, but it turned out to have too many little quirky issues (bugs) that I couldn't be bothered to waste more time with (on my primary development machine). I was constantly locking up Compiz with it enabled and getting weird graphical artifacts. Once I booted back into classic mode, everything worked perfectly (Compiz is enabled still).
I imagine some of the recent updates resolved issues, so I might try it again. It felt a lot snappier as a UI and some of the design choices are nice.
I felt it handled windows that popped up poorly, though - a number of times I would launch something, get annoyed that it hadn't shown up, and then realize it was launched, just hiding on the "dock". I never did get to the bottom of why that was happening.
Over all, Natty fixed some issues with my Dell M4500 laptop, particularly in the docking station, so it was a good upgrade for me.
Not everyone will like it, but it's definitely worth trying out.
By the way, you can stop the Launcher from auto-hiding by opening the CompizConfig Settings Manager (not included by default), going to Desktop > Ubuntu Unity Plugin and changing the Hide Launcher box to 'Never'.