I used OD (free) for 2 or 3 weeks, and was pretty content, until the coworker who showed me it in the first place, showed me the OD+ he had just bought & installed. Here's what I loved about OD+:
1. Multiple docks - I don't have to have one big dock
2. Flyouts - I can have a flyout submenu, again helps organize
3. Tabbed docks - yes, cool
4. The biggie! A stable dock that shows Windows tray icons, and not just in one docklet, but separately.
Finally, I could hide EVERY icon in Windows, and have a totally clean desktop for working. I now get the full screen.
Plus, I have been writing software for a long (long, long!) time, and I really appreciate well-done software, and advocate paying the shareware fee. The developer of a good software deserves the money.