No pointing device, which means you need an external mouse, no big deal except then you need a desk to put under the mouse. Unlike a laptop with a built in pointing device, so you can use it on your lap like its name suggests. Making that mistake in the 400 was, ok fine, a mistake. Perpetuating it to the 500 and now the 500+ just seems malicious.

And yeah, people say clip-on trackball, but I haven't seen one that fits on the 400 case and doesn't cost a bundle. Links would be appreciated.