The plug-in does let you animate your tree (wind, leaf volume by season) and you can supposedly edit the tree preset files by hand if you don't have the standalone version. You can also use parametric mapping layers with the plug-in (limbs, boughs, trunk, leaves); don't know if you can do likewise if you import a standalone tree.

Seems like the best setup is to have both and to use the standalone editor to create presets for the Carrara plug-in. Personally I think it would have been nice if the preset editor had shipped with the Carrara plug-in.

Would be nice if it shipped with more texture maps for different kinds of trees (it generates the shapes but doesn't do the texturing for you).

So far I've only been able to get trees to cast hard shadows (no shadow shows up with soft shadows).

Check out http://www.vb-visual.com/vb/produkte.php (something similar for C4D). This seems to come with lots of texture maps for different kinds of trees.

I've attached something I whipped up. Just for fun I made the tree be an Anything Glows light.

The tree plug-in is a lot of fun but it might be hard to create very realistic looking trees with it (especially without the standalone version to create new presets).