iMovie Issues / Finder issues / Dock issues
iMovie issues (Experienced on mid 2010 iMac, 2009 MacBook, Early 2010 MacMini)
. Picture in picture will add in a different picture to the one you are dragging. The clip shows the intended picture but the viewer shows a different one. In playback, no picture is there at all.
. iMovie is incredibly sluggish and on the iMac, completely refuses to do simple tasks and crashes after dragging the first clip into a project.
Finder Issues (Experienced on all machines above)
. Dragging a file from the Finder window into trash causes the window to lose its left-hand side menu and for the column adjacent to it to be half in and out of the left hand frame. Dragging the window side or scrolling horizontally within the window doesn't resolve the issue. Closing the window and reopening it puts it back to normal. Right click 'Move to Trash' doesn't cause this problem.
Dock Issues
. I have the dock hidden. When using some applications (typically Safari), dragging the mouse to the bottom of the screen to reveal the dock simply doesn't work. I have to change to a different application to be able to show the dock. On a few occasions, I haven't been able to get the dock to show even when I only have the desktop screen and no applications open immediately after booting up or restarting the machine. Again, setting the dock to not be hidden and then turning 'Dock hiding back on in the 'Apple' menu resolves the issue in most cases.
Not having a good experience with Lion at all.

I wonder if it is possible to reinstall Snow Leopard? The recent update was not very helpful other than it did solve the Wi-Fi issue on the iMac.