I've been toying around with this configuration lately. It seems like a much better setup if one can get used to using the mouse with the left hand. Here's some advantages:
-Alphanumeric keys are now centered on desk, instead of being pushed all the way to the left. Much more comfortable considering both hands use these keys!
-Mouse much closer to a hand (even closer than tenkeyless due to lack of arrow keys.)
-Right hand can be use arrows and numpad while left hand uses mouse. Useful for data entry, especially in places where tab key doesn't work.
-If you're right handed, allows you to write, drink coffee, etc... while using mouse.
-Less people ask to use your computer
The problem, of course, is the learning curve. I'm left handed, but I'm so accustomed to using a mouse right handed that it still feels weird. Also, you need a mouse that isn't designed for the right hand.