I haven't considered my laptop as a main machine. However, on occasion, I went to the beach for extended hours and used my laptop. During those occasions where I used my laptop for many hours it worked reliably.
Using a laptop as your "main" should work great. Do remember though that in order to use a laptop as a main machine, you should keep it plugged in all the time. Battery power won't last you more then 8 hours and you would wear out your batteries if you constantly had to recharge them. When thinking about using a laptop as your primary computer, also consider the screen quality. Is the screen big enough? Will you experience any eye strain if you look at the laptop screen all the time? You may want to get a docking station instead, and hook the laptop up to the docking station, and use your current screen, keyboard and mouse thru the docking station.