Looks useful. Maybe under the "moisture" dropdown you could add a "mediterranean" option (alternating wet and dry seasons)? Also in the moisture dropdown, "well-drained" could be a characteristic of any of the other moisture options ... perhaps that
should be a different dropdown altogether (i.e. "drainage:" slow, medium, fast).
Along these lines, I've though before that a Guild Generator could be a useful tool. Imagine a database containing something akin to the data in the appendices to Jacke and Toensmeier's
Edible Forest Gardens. A user could enter search criteria (climate zone, moisture, light, etc), and the tool could spit back all plants matching those criteria. The user can then sift through this list to find plants that might be appropriate for her guild. It wouldn't be a substitute for careful observation and
experience, but it could help narrow down the number of plants that might be appropriate in a given situation, or offer suggestions that one might not otherwise have thought of.