I did the Ethernet set up tonight for the first time (unrelated to this thread - I wanted to try it as a means of being able to edit some photos as I shot for a gymnastics meet, especially after reading about its use in Sochi). It takes a few seconds to transfer RAW files, and if you run out of space on both cards it can cause problems - I waited till one card had cleared, hoping to format it since I had all the files transferred as I filled the other one to the max. It would not format and the upload broke for a spell when I pulled the first card so I could keep shooting.
I had to restart the upload at that point. But the system was very dependable and after a bit of getting used to it I found it to be fairly easy to work with.
I can't wait for the D4S however as Gigabit Ethernet will make RAW file transfers much faster. When shooting a gymnastics meet, I found the D4 and its 10/100 Ethernet falling behind on the transfers a bit.
Still it is a great option in the right circumstances. For Basketball or gymnastics it should be very useful and I expect it to work well for baseball too. I'd guess Soccer (or futball to the UK folks) would be good if you had a place to stash the laptop and access it.
Notes: I was using a MacBook Pro with OS X 10.9.2 and recently installed Wireless transmitter Utility from Nikon, which is needed to get the setup up and running, as is a USB Mini to USB standard cable for pairing only. Current Photo Mechanic live ingested from the standard Wireless transmitter Utility folder. Works like a charm on Photo Mechanic's end.