I'm almost in the same boat. The Mac OS player doesn't buffer either while the PC player does. I used that buffer religiously when overseas due to slow internet but when I changed to a Mac laptop lost that ability and about 60% of usage.
I'm now looking at using slingbox with my iPad Mini so I came to do some research and have found this issue to be very important. Why hasn't Slingbox answered when this question was asked back in November?