I've found that the notion of the "Ideal Customer" is only useful when I'm able to line up the expectations of that customer with what our product can actually deliver. When I've been able to refer to that customer during the product design process, the results have been good - i.e. I've been able to market successfully to other customers that match the profile of the Ideal Customer. However, when I've tried to use the notion of The Ideal Customer to create marketing positioning that didn't necessarily line up with the product, its been a dismal failure - i.e. the customers I managed to attract eventually discovered where I had "spun" the story and they either passed on the product or didn't turn into long term customers.
Over time I've realized that the easiest way to make sure people are buying product from me is to make sure that what we're selling is what we've built and to make sure that those Ideal Customers have been taken into account every step of the way.