We already know, as evidence by the VX Nano, that Logitech knows how to make a desirable portable mouse. Little did we realise, though, that it could take that concept and run with it all the way past desirable into the borderlands of crazy. With the V550 Nano, I think that trick has been pulled off.
The V550's party piece, so to speak, is the inclusion of the 'Clip and Go' dock, basically a clip which is attached onto one's notebook to which the mouse is then clipped. The idea being you don't have to carry your mouse and notebook separately, because you can fasten the one to the other while transporting it about - quite why you'd want to is another matter.
Battery life, however, is unquestionably good at a claimed 18 months use! Further to that, the V550 sports Logitech's Nano-receiver, as introduced alongside the VX Nano. The idea being that the transmitter is small enough to be left inside a USB port and forgotten about. There is a recess in the mouse for storage, should you need to free a USB port, though.
The clipping might perhaps be considered a bit of a gimmick, but in every other respect the V550 Nano should make a fairly serviceable addition to any laptop bag. The only real downside is the £49.99 MSRP, the same as the http://www.trustedreviews.com/peripherals/news/2007/07/27/Logitech-Breaks-Out-VX-Nano-a-mini-Revolution/p1. I know which I'd rather carry around with me…