Having used a Bluetooth portable mouse for some time I can tell you it’s nice to carry a mobile mouse around without any receiver to keep track of.  Logitech has recently announced their portable mouse that connects via Bluetooth and it looks pretty sweet.  The V270 is based on the Logitech Cordless Optical Mouse for Notebooks but uses Bluetooth instead of the separate USB receiver.  Pricing should be around $50 when it is released in November.