It's worth remembering that health and safety rules prohibit employers from providing their employees with laptops, rather than desktops, when they'll be doing all of their work from a single place. That's because the way that people sit when using laptops (and the position of their arm when using touchpads) can lead to nerve or muscle problems through extended use.
Obviously such rules don't apply in the home but anyone who chooses to use a laptop for long periods at home shouldn't be surprised when he/she develops wrist, arm, shoulder, neck or back problems.
I much prefer to use a desktop. They also offer better options for upgrading or for fixing things when they go wrong. (If I spill coffee over my desktop's keyboard I can replace it for a fiver. If I do the same with a laptop it could cost me far more money).
Further, I like to do quite a bit of image processing, which means that I value having a monitor which is perfectly set up. I can tweak the brightness, contrast, colour and gamma settings on my desktop's monitor to achieve perfection; I can't do that with laptop screens.