With 17" screens already at 1920x1200 I wonder what's left in the more real estate. You cant display more information on a 17" at 1920x1200 then you can on a 20" notebook at 1920x1200 the only resolution higher is 2560x1600 and that's really quite big and doesn't come in any size below 30" at this time.
I can understand people wanting a physical display size of 20" but if it only offers the same resolution as a 17" then I don't personally see the point. The reason Laptop monitors are at such a higher resolution to desktop monitors is because you sit so much closer to the screen. With the monitor taking up more of your vision things can be smaller because your closer to view them.
I think personally a 20" Notebook is pointless if it offers the same resolution as a 17". Perhaps if you want a desktop replacement but in that case just buy an iMac it would likely be 1/3rd the price and lets be honest the iMac isn't exactly a sack of bricks its a very small and easy to move computer. And I know people will say well what if I want to take it to Classes! I cant take an iMac with me can I? - To that I say are you really going to carry a 20" Notebook everywhere with you?, likely weighing 8 pounds due to the heavy duty screen supports and just in general the sheer size of it. No I didn't think so.