i have only just completed my first front wheel build and have prolly clocked about 100 miles on it so far. I have put well over a 1000 miles on a variety of rear wheel builds.
My experiences (similar to others based on the comments/responses to your thread) are that the front wheel is fine for the kinda surfaces/work you are looking at, firm, relatively smooth, unlikely to have either the bike airborne, or trying to get up a 50% hill with dubious traction
I am now a front wheel convert after using the current front wheel build purely as a shared cycle way/road/ foot-trail commuter. Main reason... I can keep or upgrade the rear wheel and human powered gearset, so can work on maximum efficiency on the pedal powered front without having to compromise due to restrictions on freewheels, space, brakes, and wheel size.
BUT I would not be even vaguely inclined to Jump a front wheel build or do the dubious surface sharp incline thing unless under duress, whereas with my variety of rear wheel builds, I takes off road and does stupid things with them all the time.
Here are some details of the Front wheel build I am currently working with.http://frankencycle.wordpress.com/builds/pocket-rocket/
The motor is rated as 500w at 24 volt, the battery is 24 volt 15ah, the frame is steel, ex "hybrid" with a 700c road rear wheel and freewheel fitted.