I have the newest model of Macbook Pro with the 750m, running Mavericks 10.9.2 and After Effects 220.127.116.11.
When the 750m was active, After Effects was exhibiting an issue where when a layer's opacity was dragged to zero, it would gradually become transparent as expected, but snap back to full opacity when 0% was reached. Restarting After Effects, restarting the computer, clearing the cache all failed to fix the issue.
On a lark I downloaded a utility to force the integrated graphics, and upon doing so, the opacity started working correctly again. Moreover, Ihave since switched back the 750m and things still seems to be ok.
I guess I'm posting this to a) to hopefully help anyone else who encounters this, and b) to document it in case it turns out to be a recurring bug so it can ultimately get fixed!