I think 37signals has it right with making things simple, and emphasizing simplicity, at least on a first use basis. But I still maintain something that Guy Kawasaki said in his book, art of the start…
I’m paraphrasing, but basically simple for new users, but deep for veteran users. There’s something to be said about keep mastering a product over time.
New users, no matter how tech savvy, like simple to use. But there’s something to be said for the constant exploration of a device (or domain for that matter). I liken it to driving stick after learning to drive automatic.
It’s often hard to build the two conflicting things in a product…control vs simplicity. But I think it’s important to think of deepness as well.