After upgrading to Ubuntu Lucid, I didn't like some aspects of the new theme (Ambiance). Here the fixes for the two of those things.
Move minimize/maximize/close buttons to the right side
With the new theme, the three buttons to minimize, maximize and close the window have been moved to the left side of the window. To fix this, issue this command:
$ gconftool-2 --type string --set /apps/metacity/general/button_layout ":minimize,maximize,close"
A panel wider than 24px looks ugly
Another thing is, that the background image for the panels doesn't scale (See Launchpad Bug 532309). To fix this, edit the file /usr/share/themes/Ambiance/gtk-2.0/gtkrc and comment out the line bg_pixmap[NORMAL] = "panel_bg.png".
#bg_pixmap[NORMAL] = "panel_bg.png"
As an alternative, if your panel is exactly 30px wide, you can also replace panel_bg.png with panel_bg_30.png.
bg_pixmap[NORMAL] = "panel_bg_30.png"
After that, log out and then log in again, and the panels should be fixed.