Mice are better without their tails -- Going wireless lets you get untether from your computer and get rid of those clumsy and tangled wires. Systems like the new Logitech Anywhere Mouse MX even support keyboards and multiple mice to really trick out your system on your desktop (see previous post).
Mice are also better without an additional dongle. Many wireless peripherals use a proprietary 2.4 GHz wireless connection, which means you need to plug the matching receiver into a USB port on your system. For notebooks on the go, that's just one more thing to break or lose, and it blocks off the USB port, which you may need for attaching other devices like an external hard drive, digital camera / camcorder, or smartphone.
But there's another way to do wireless that's become quite ubiquitous and quite reliable, and is probably already built in to your laptop -- Bluetooth (see Wikipedia). Proprietary wireless technologies have advantages under heavy loads and in difficult environments, but plain old Bluetooth is quite good enough to handle mouse movements -- and it does not require any separate receiver / adapter / dongle.
For example, the Verbatim Go Bluetooth Wireless Notebook Laser Mouse is designed for use on the go. It's compact but not tiny, to fit comfortably in your palm.
And it has some interesting additional features: The scroll wheel also tilts, for left/right motion, and the power/status light doubles as a DPI / speed control button, to switch sensitivity between 800 and 1600 dpi without requiring any software configuration.
As a bonus, if you've never taken advantage of Bluetooth on your system you'll discover some additional fun options from the universe of Bluetooth peripherals. For example, you can play music wirelessly to your Bluetooth cell phone headset (or even a Bluetooth headphone), so you can listen in public places without disturbing others.
However, there is one more step required with Bluetooth: unlike the proprietary wireless systems that connect automatically, you will to run the Bluetooth manager software on your system to enable the connection, and then go though the discovery process to link with each new device.
See my Portable Peripherals and Accessories Gallery for more on these and related products.
Find the Verbatim Go Bluetooth Wireless Mouse on Amazon