I have been using this for a few weeks now as part of an evaluation for tools and tricks for the left handed tablet user. I have found that the simple vertical and horizontal gestures work the best. Anything much more complicated produces an 'unknown gestures' error. You can customise or produce your own gestures but I haven't ventured that far get. The gestures that I use the most are backward, forward, new tab, previous and next tab. Out of five I would give a score of four.

i've used this for more than a year. no problems, works great. like most people i expect i only use a small handful of the gestures. although the customization screen is a little complex, I did manage to customize one of the gestures to my liking. my 10-year old uses it regularly as well with no issues.

Partial repost of my comment at jkOnTheRun (minus my jab at Kevin for not commenting that I mentioned gestures to him months ago at Kevin 2.0. This jab is all-new, as is this mention that I've blogged about making Firefox pen-friendly. :p ):

But seriously, one feature really worth mentioning for UMPC and small screen PC users is the ability to gesture the Full Screen command. Gives you maximum window space while retaining tabbed browsing and you can navigate without buttons by using gestures.

I've been using an IE version for years. http://www.ysgyfarnog.co.uk/utilities/mousegestures/