The trackpads on netbooks and laptops can often be uncomfortable to use, especially if you use them for long periods of time.
A good solution to this is to get a separate mouse that you can use alongside your laptop. This can bring its own set of problems, however, because if you don't have a desktop, where can you use your mouse?
The Logitech Anywhere Mouse MX's answer to this lies with its 'Darkfield' technology, which allows this mouse to be used in places and on surfaces that most other optical mice fail dismally at.
It works well, with shiny surfaces, glass and even laps making adequate mouse mat replacements.
It's quite a small mouse, which makes it easy to transport (especially considering the carry case that's included), but it's not the most ergonomic mouse to use.
If you work at your desk for long periods of time, this is not the mouse for you. But if you're often on the road and need a mouse to make using a laptop easier, then this is definitely worth considering.