For a product just shipped, I needed to separate a single horizontal toolbar into 2 distinct parts: the first for file operations, the second for editing/navigation operations.
Because I added the file operation buttons last, I hadn't added the code to paint the gradient on these for the '3d' effect. It then occurred that these new buttons had a subtle 'sunken' quality that helped differentiate them from the rest.
The other 'benefit' seems to be that the right part of the toolbar appears as if it could slide over the top of the left part (to reduce clutter). Does this work, or does it seem too contrived for what's a simple toolbar?