Can A Treo Really Replace a Laptop?

I'd like to propose a simple scenario to you. What if your computing devices consisted of a laptop and a Treo-style Smartphone? You use the laptop to do all the normal computing tasks, as well as some extras such as play games or some sort of development work here and there. You have your Treo as a main data organizer and means of email management when out and about. You do the occasional budgeting and gaming, but for the most part it is an assisting computing device.