Even a visit to the Genius bar had not worked.
OK, first check - Are you using Wireless ? If you are, just to verify you have the same issue, turn off wireless security temporarily and re-connect both device wireless connections.
Second, what they don't tell you is that you have to go to System Preferences, Sharing, add your user account, say "FRED" into the list of Shared folders, then specify who is allowed to use them. You have to do this on both computers.
Third, with wireless security turned off, you should now be able to see the other computer in finder and you should also see that Home Share works in iTunes provided you have also followed the setup instructions for Home Share in iTunes.
OK, if that works, and you can see the other computer and search directories within Finder and also Home Share within iTunes, then go back to your wireless security and turn it back on. The mode does not matter. It should work fine with WPA2 Personal contrary to Apple stating that File Sharing only works under WEP (they simply have never updated the page).
Now, what you will find is that you can see each computer in Finder but when you click on the icon for the other computer, a dialogue box comes up saying Connecting but it fails to connect. At the top right hand corner of that dialogue box, there is a 'Connect As' button. Click it and another box comes up asking you for a user name and your password. This, on my machines, is the same as the password you use when the system jumps in if you're installing software and asks for a password. Type in the required details, click the accept button and, within a few seconds, mine was working Ok and Finder displayed everything I needed on the other computer.
You then need to go to the other computer and go through the same process so that each device can see the other.
This is nothing short of a huge cock up in iTunes as they lead you to believe it is totally independent of file sharing and wireless security.
Hope this works.