I'm trying not to hate Unity, but I'm still not in love.
If I have windows non-maximized, I often find that the window is stuck so the title bar is hidden by my Unity top bar. I had to enable Compiz's Window Management Grid just to give myself ctrl-alt-num6 as a way to force windows back into the visible screen.
Is there a way to keep windows from slipping up under the top bar?
You need to set the appropriate option in the Compiz Place Windows plugin.
This option is usually set by default, but sometimes for some reason it is not. I am not 100% certain as to the cause (still trying to find it). If you do not have the place windows plugin, make sure to check that you have any additional compiz plugins installed in the software center.