Improve theming (see grouping indicators for dark/bright bg decisions plus stackoverflow)
Ensure workspace wrapping when scrolling is the same as general workspace wrapping (possibly offer a setting in the properties dialog) - currently we ignore wnck wrapping
Add more options to workspace cycling (including disabling it, if libwnck allows for that)
Look into getting app icons at different icon sizes (libwnck patch?)
Grouping
Move grouping options to a separate - dynamically added - tab
Offer more options (hide group indicator, possibly re-add text style)
Add option to keep mouse-wheel cycling within the group (so you switch between the windows of one application only) - or adjust the cycling logic to prioritize groups