It's crazy how many OSX features come from the unix world but in a delayed, better looking fashion.
The last missing major piece for OSX was good multiple workspace management, which came in the form of mission control and the touchpad gestures that makes it so efficient. I don't know if its any good with a mouse though.
Efficient multiple workspaces is a critical productivity feature for me. It's like having multiple monitors without having to carry a desk and a bunch of monitors with me all the time.
The previous OSX implementation called 'spaces' took too many actions to switch workspaces unless you had your hands on the keyboard and had setup shortcuts. This made OSX unusable to me.
Unfortunately, Ubuntu also regressed by getting rid of the single-click workspace switcher (which was working beautifully since like 1995) and doing a multi-workspace UI that resembles Lion's 'spaces'. However, I was able to remedy this by setting my middle mouse button to bring up the workspace switcher which is really fast.
The other Ubuntu regression which annoys me to no end and again is the same in OSX is that clicking on a dock icon when you are in a workspace and there is an instance of the app opened in another workspace makes you automatically jump to the other one instead of opening a new instance in the current workspace.
This assumes I separate applications on a per workspace basis which is stupid. I already have a dock to get access to different applications. Workspaces are used to separate projects or workflows.
Each workspace needs its own browser window that holds the tabs related to the project being worked on and also its own terminals and text editors. I don't want to be yanked out of a context because I tried opening an editor and there wasn't one already in the workspace.
Hopefully this is eventually fixed in both OSX and Ubuntu.