Here's a quick debugging tip if you're having trouble getting Back to my Mac (one of the MobileMe features in OS X 10.5) to start up. You click the Start button in the MobileMe System Preferences panel, but on one of the machines, nothing happens, and the button returns to read Start again.
It turns out this problem may be caused by differences between the clocks on the two machines. Back to my Mac uses Internet Protocol Security (IPsec) to connect your Macs to each other. IPsec requires that the two machines have identical (or very nearly so) clocks in order for this to work.
The easiest way to make sure both clocks match is to set both Macs to set the date and time automatically. Open the Date & Time System Preferences panel, click on the Time tab, and check the Set date & time automatically box. The text field should then indicate that it's going to use time.apple.com to sync the clocks. Let the clocks sync, then try Back to my Mac again.
If you'd like a more-robust time server solution that works in the event that time.apple.com ever goes offline, check back at the Mac OS X Hints blog this coming Friday for a more-geeky approach to identifying and using time servers.
This story, "Solve an Obscure Back to My Mac Issue" was originally published by Macworld.