I've just used one panel for yonks. One thing I used to do with GNOME 2 on my wide-screen format laptop was to use a side-panel instead. The wide-screens so typical these days tend to leave you with a surfeit of horizontal space relative to horizontal. On smaller wide-screens you may even be short of vertical space and not want a top-panel at all (or at least, if you do, have it set to auto-hide).
Configurable side panels and auto-hide have been excised with GNOME3 AFAICT.