While many in the media have complained about MobileMe's new Back To My Mac feature as not working or unusable I say it is great step in the right direction. Don't get me wrong there are a lot of things still lacking in MobileMe I would love to see happen to give me more seamless access to my data.
First the Back To My Mac feature has worked very well in networks where outgoing ports are not blocked. UDP 4500 and TCP 443 need to be available for Back To My Mac to work on OS X 10.5 Leopard. Currently I have a G4 Tower, Macbook Pro, and an account on Mom's Powerbook G4. All of these machines show up in my network list in most places I go and I can easily access my G4's hard drives or use Screen Sharing to access the desktop.
Now with the latest update to my Airport Extreme base station I can now access my file share on that device wen I am away from home. The limit being it only supports one Mobile Me account and our family has two Mobile Me accounts. So only one of us gets access to the Airport Extreme while away from home but it is a step in the right direction.
Since I have an account on Mom's laptop since I used it while mine was being serviced last year I can Screen Share here computer where ever I am with a network connection and remote control her computer and help her with issues she might have or answer questions about her Mac.
To make this work well. The first thing I did was plug my Airport Extreme WAN port into my cable modem. My Vonage router plugs into the LAN port on my Airport Extreme and works great. If you are using a Linksys or Netgear device then look at NAT-PMP (Network Address Translation - Port Mapping Protocol) or UPNP (Universal Plug n Play), or open the TCP 443 and UDP 4500 and point them at your Mac. As long as there is nothing preventing outbound traffic while you are away from home and your computer doesn't go to sleep you should have access to your Mobile Me.
If you have questions or issue with your Mobile Me drop me an email or comment and I will take a look at it.