It's hard for me to know when to harvest eggplant, too. I think that once the skin turns dull they are overripe (???) If you don't see a lot of green near the stem end then I think you can harvest any time. But I hope somebody else will have a more definitive answer to this question! I have quite a bit of eggplant out there, though no where near ready to bear fruit. (In my opinion, the skinny long ones are the TASTIEST!!!)
Purple hull peas--when you find out, report back, as I would like to know!