Andrew,
Looking forward to seeing your board. I've thought about doing something very similar.
What sort of a tank are you running those luxeon LEDs over? I'm likely using LEDs for the main lighting on all my reef tanks for the foreseeable future, and have a driver designed around the OnSemi NCP3066 that I'll be using. Perhaps not as simple as a linear reg like you're using, though.
For those looking for an I2C LCD driver, there are a few other vendors selling them, including this place:
I have no experience with them, but figured it was worth mentioning since it seems people are looking for this functionality.
I'm considering just using an I2C slave RBBB attached to the LCD in parallel (with the LiquidCrystal library to control it). This will cost about the same as a dedicated driver, but also give me extra PWM pins, analog in pins, etc. though of course there will be a fair amount of coding to do. . .