I've used Oversite since 2.x, and recently upgraded to 3. For me it was well worth the upgrade. Most of the new features are in the wireframe tab, which is where I do most of my work. The new editing panel that's next to the wireframe canvas by itself is worth the upgrade cost, since it eliminates the one annoyance I'd had with the older version: model edit dialogs. The new panning and zooming, plus some new complex components, are icing on the cake.