Depends on the person. I didn't have anything to do (as usual) and I HATE the hildon UI so I had a go at skinning. I've done it for my mobiles and that was easy, as the application generates the images for you but I would only advice people to skin a N800 theme if they are very knowledgable in Photoshop or any similar program like Gimp, as you need to be very organised and know how to use layers and what tricks to do.

All you're doing is making your image over the template, sounds very easy but VERY hard, as you're working with pixels rather than vectors so to do a minor edit to something you might need to take your time and zoom up like 600% and edit pixel by pixel.

Also the template is only the begining and is only 75% of the UI which is skinned, the rest is all down to you editing the gtkrc file for example.