Very nice start indeed! Very intuitive, features make sense, program seems to work as advertised. Features I would include/add to the list:
Linux/Android support would be first on my list. Check out the Android developer API, it makes things wicked simple and gives you a lot of cool options, and Android is also poised to take over the smartphone market. It is also much more OPEN than apple's products.
Sensors support has a lot of potential. Heat, humidity, Co2 sensors with reporting capabilities via SMS, email etc. That would be badass and the possibilities are mind-boggling. Maybe before that, a simple interface for tracking heat/humidity/co2 etc under the Grow Room tab. I know where I live the temps swing dramatically from season to season and it can have a big impact on the room, and an interface for tracking that would help anticipate the needs of the room during different parts of the year.
Extra security measures, auto-data wipe, strong encryption, etc. This is another good reason to add Linux support.
I know a lot of people are on their high medicinal horse but let's not forget our brothers/sisters in non-medicinal states!
On the nutrient page, how about a simple calculator and possibly a feeding schedule? Maybe PPM, EC, PH tracking with graphing capabilities? Something to keep track of what you feed them and when. Maybe even give an interface to input the exact guaranteed analysis of elements on your particular nutrient product, then do the calculations automatically based on reservoir size, desired potency of the solution, etc.
That said I think you have an AWESOME feature set so far. You get my vote right out of the gate just for being open source!
I will keep a close eye on this project and give you feedback/ideas as they come to me. Sorry if anyone already asked for these features as I really don't have time to read 50+ pages of this thread right now.