yeah agree. Another cool metric is "if your idea can be given away by telling someone" then it doesn't have enough depth" Most simple things are way more complicated when u do them - and thats in the thought of the implementation.

Just look at eBay - a platform for auctioning goods. The depth comes in generating a trust system (how?) then making it easy to list, and for people to send each other goods. Then each of these ideas can be fleshed out. So its not really one idea - its a whole bunch including design decisions, customer acquisition strategies, page element preferences, copy, bug fixing - a whole load.