Excellent plugin - many thanks for your work on this Zack.
As best practice, I wonder if the 'termmeta' table that is created by the plugin should be prefixed e.g. zt_termmeta?
Also, just wondering aloud, maybe this plugin could be extended to include the ability to store a category image reference? In a theme I'm working on, I currently associate category images via an entry in the options table and echo via a call to get_option(). With your plugin already creating a new table, would be great to store all term meta data in one place and reference appropriately e.g. term_id = X, meta_key = tax_image, meta_value = smile.gif.
Anyway, just a thought. Once again however, thank you for a wonderful plugin.