Wacom Bamboo or Intuos4 small for portability?

I know there's another tablet thread, but I didn't want to hijack their thread.

I have a MacBook Air 11" which is mainly for writing and web surfing, but I've been trying to do a little design work on it and I'm having a heck of a time on the small trackpad. I think getting a small tablet would help greatly... it needs to be pretty small and light itself though. I have an Intuos4 medium for my desktop and love the thing. Would the Bamboo suffice or would I hate it being use to a Intuos4? And is the Intuos4 small, actually pretty small? Like easy to carry in a messenger bag?

Thanks for the help.