Turn IS Off?????????????? (Sports shooting)

So I've had my 70-200 f/4 IS for a few weeks now, and have been using it at my kid's soccer games. I'm pretty pleased with the results. My biggest problem is holding that center focus point in the right spot.

These games are in broad daylight. I turn the ISO to 200 in Av mode wide open at 4.0. Therefore I am usually at or faster than 1/1000.

Now I know that IS is NOT made for these situations, but I have always figured that it couldn't hurt, and would likely be neutral. (I bought the IS version for indoor use, slow shutter speeds and the rumored better optics.)

Now, I've read another thread where someone said that leaving the IS on in these types of situations could be bad for the final shots (i.e. the lens' IS system can't keep up with these fast shutter speeds).

I'm very curious about other people's thoughts.
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Just a weekend hack...

Rebel XTi
Tamron 17-50 - 2.8
Canon 70-200 f/4 IS
430EX