Compiz regularly crashes, but thankfully it automatically restarts. Now I don't need to panic when the whole screen stops updating.
The "snap" window dragging feature is broken in the presence of multiple monitors; as you drag the mouse across the monitor boundary, the mouse pointer becomes momentarily disconnected from the window location, so that you are moving the window as if by a long invisible stick, not by its original grab location.
The overlay scrollbars don't interact well with Eclipse; JUnit running tests outputs file paths that Eclipse turns into hyperlinks, and the hyperlink mouseover stops the scrollbar from from being triggered when the pointer approaches the child window border. The overlay scrollbar thing doesn't seem to have been fully thought through.
Gnome-terminal is one of the slowest terminals I've ever used; it would literally slow down development by blocking on log-verbose tests. I've gone back to my old stalwart of rxvt.
I don't understand the difference between Windows key and Alt key command prompts. I've given up trying to figure out how to register my various user-directory installed applications with the taskbar thing. So I've stopped using both, and now I start all my apps from the terminal, with shell scripts to redirect output if they are chatty.
The Alt-Tab task switcher is broken just like the OS X one is, switching between its concept of applications rather than top level windows. This means alt-tabbing between Eclipse and Firefox would bring the Downloads window to the fore, leaving the actual browser hidden behind maximized Eclipse. Usability disaster. With some difficulty and playing around with preference managers that come with warning labels, I've rebound the keys to a slightly more usable window switcher.
Oh, and the fun I had when I tried to bind Ctrl+Alt+F12 to a command in Eclipse; took me back decades to switching terminals with Alt+F keys.
In short, Ubuntu Unity is horrifically bad. Linux is completely inappropriate for the desktop, unless you are so inept you only use a browser (get an ipad instead), or you are sufficiently skilled you think nothing of switching window managers. The trough in the middle is very ill served.