Not able to Ping to MacBooks?
I have not seen this issue before. I unfortunately can not duplicate this issue at my office. Two MacBook Pros and a MacBook all respond to ping requests. All units are running Mac OS X Lion 10.7. I used Network Utility to preform the ping to the IP address and host name.

About how old are these computers and do you know the model name? What software is running on these computers? What software are you using to ping the computers? Are you pinging the IP or host name? If the Apple Firewall is off, do you have any other software running for security? What router are you using? Is there a firewall in the router or a feature such as 'wireless isolation' turned on? If more than one router or switch is involved, are the computers on the same subnet? Are these computers wirelessly joined or wired to the network?

I would think the answer to the problem would be found in one of the questions I have asked you.