My first contact with Unity was when I was trying out some Ubuntu netbook distro, but that wasn't more than few clicks. I liked it then as an idea, but now it has become reality for many. I'm using Unity on a laptop without touch screen. On touch screens there are probably other pluses and minuses in addition to mine here.
Plus : More space on my small laptop screen. I like the way launcher bar, application status bar and menu bar are all combined in one row on the top of the screen. That alone saves quite some pixels of valuable space.
Minus : Launcher menu takes a second to open. I don't mean a second, as in fast, but literally a second. To wait one second every time you want something from you computer is annoying to say the least. This is probably because Unity is based on Compiz which, when I enabled it for a short time in some previous version of Ubuntu, slowed down my desktop significantly. From then on I make a big circle around Compiz. I found a setting, that a launcher can be opened when mouse cursor is at the top left. This way it's faster, but it's also more limiting. Maybe I'll get used to it.
Plus : I like color coded status "messages" from icons in the notification area. Applications like Gwibber and Evolution interrupted my work, whenever that big popup window appeared, with a message shining to my face. Now it's better. Just a small unobtrusive change of color informs me something is going on, but is really not flashy enough to interrupt my work.
Minus : Opened terminal from the really cool launcher menu on the left and connected to a remote machine via ssh. What I like to do is then open another terminal to scp file to remote computer, then handle those files in the first open terminal, with ssh connection. But click on the launcher menu starts an application or bring it to focus when already started, how do you then open another one? You click with a middle mouse button. That, which I don't have on my notebook. Another way is clicking on the Ubuntu logo on the top left, enter name of application you want to start and enter. But this is then already as good as if I was working in terminal, I don't need GUI for this. That's actually complicated enough that I started to use Terminal as it's supposed to be used. I open new tab from menu :)
Plus : I love new scroll bars. They are there only when I scroll. When I do not, they don't take screen space. Such a simple idea, so obvious, how come we didn't have this earlier?
Minus : Still doesn't work in virtualization environment. Here I'm talking about Windows 7 as host system, running VirtualBox 3.2.12 and Ubuntu 11.04 with Unity as guest OS. But then the Ubuntu 11.04 by itself just defaults to Gnome 2.32 and Unity stops being a problem. Although, why Gnome 2, when 3 is released already? Maybe that will change too in future, if not Unity compliance to virtualization. (Edit: tried with VirtualBox 4.0.12 and reproduced this.)
Minus : It is not possible to move Unity launcher to the bottom. I know it's not a functional issue, but I would really prefer it on the bottom of screen. Maybe in time, I'll get so used to having it on the left side, that I will also start to prefer that way :) Until then, this is a bad thing.
Edit: minus : Can't pin Netbeans application to launcher.