My FTC team (72) used a slide drive base(inspired by FRC148 in 2010, sans traction pods) up until our first competition. (The video linked above in Techhexium's post).
Personal experiences:
As driver, I found that it helped a lot with lining up for scoring, but we did have some traction issues. The mountain in the middle of the FTC field was difficult to traverse with these wheels. Seeing as though VEX Gateway's field is flat, this may not be a problem for you.
In the end, we scrapped the drivetrain after deeming it unsuitable for our strategy of traversing the obstacles.
As with the choice of drive train(or any system, for that matter) in any robot competition, there are a series of pros and cons.
Pros:
Maneuverability - 3 degrees of freedom: X Translation, Y Translation, and Yaw vs 2 degrees(Y translation, Yaw) of a typical skid steer drive
Faster scoring in autonomous mode - The robot is not spending too much time turning and driving... turning and driving... etc, just translating along the X/Y plane and only turning when needed.
Cons:
Loss of traction - omni wheels of any kind typically have a lower Coefficient of Friction wheels
Complexity - More motors, transmissions, etc
Weight(only a real issue in FRC) - See complexity
Regardless of platform, you also have to worry about your chassis flexing. You might remember from Geometry class that between any three points, there lies exactly one plane. With Vex or Tetrix metal, it is relatively difficult to make all 5 wheels(left 2, right 2, strafe) touch the ground. Depending on where the flex is, you might have trouble strafing or translating across the field. Also, on that note, weight distribution is key to ensure the robot moves as desired. For example, if more weight is on the two front wheels and less on the back and strafe wheels, the other wheels may begin to slip.
I highly recommend implementing a form of speed control on the wheels. Search CD for threads about speed control and mecanum drive trains if you are interested.
Also, like all drive trains, slide drive could only be used to its full potential with practice. No use giving it a strafe functions if you drive it like a tank, right?
If you have any more questions about FTC072's experiences with the slide drive system, you can PM me.
Look at the problem and find the simplest solution. Don't look at a solution and try to find a problem to solve with it. - apalrd [more] 
Hybrid Mode
