Well.. don't have any numbers but I have a few years of experience using a laptop.
The main thing when it comes to ergonomics is that you are relaxed, i.e. that you don't strain one or several muscles to handle your computer.
One of the most comon suggestions is to keep your elbows to your body and that your underarms are resting comfortable as well as your shoulders. A laptop is very good in your lap, since it's the perfect height for your upper arms to rest comfortable while you rest your lower arms on the arms rest on the laptop and it's even better with it's mousepad in the middle since you don't hold out your left or right arm to work your mouse.
So if you're sitting by a desk you might need to find the perfect height for your desk so that your upper arms are nice and relaxed to your sides and that your under arms are relaxed aswell and not in a weird position. When it comes to sitting on a chair it's the same rules as sitting on any chair, either your work with our without a computer at all.
Both on laptops and on stationary the ideal screen height is that you have the top of the screen in eye level, that means that you're not bending your head upwards and get a stiff neck, and it shouldn't be too low either since you then would get a stiff neck aswell. And it happens to be that the laptops are in that height automatically when you have your laptop in your lap. So there again it's important to find a table in the right height to view the monitor (and not stress your shoulders and upper arms).
This is what I've learnt during the years, both with working with laptop computers as well as stationary machines.
Oh, and if you have one of those nice desks at work where you can rise the table so you can stand, do that at least once a day, that's good for your back. Sitting on a chair too long is never good for any body.
