One word - laptop!
I've owned the corded version of this model for six years now, and still use it, simply because it is the best in comfort, precision, ergonomics and durability.
I actually wrote an article a while back on my blog about trackballs:
http://lgponthemove.blogspot.com/2009/11/tech-tips-6-trackballs.html
My only wish now is for Logitech to make a BLUETOOTH VERSION (!!!) that I can use without the silly USB dongle. That said, I'll be picking this baby up as soon as it hits retail - the luxury of not having to deal with wires when I'm on the go all day with my notebook/netbook will be sweet!