I think they need to add a wish list section to the marketplace so that users can keep track of apps they would like to buy, but maybe can't afford right now, or don't have space for at the moment, etc. In addition to try/buy/install buttons on an app's marketplace listing, add a "pin to wish list" option. I think this would be a nice addition, and I think a first among the mobile platforms. Could even allow sharing of wish list so others could gift you apps you want.