I came across something that is apparently being overlooked by the Windows based Thunderbird community. If you don't know, Thunderbird is a cross-platform, open source, feature rich email client.
Windows isn't quite a first class citizen with Apple's MobileMe (yet), but it is a lot closer than it was when the service was known as .Mac. With MobileMe on Windows you can sync your MobileMe Address book with the Windows Address Book, which is used by Outlook Express. If you tell Thunderbird to use Outlook Express' Address Book as a source for contacts (LDAP), any changes you make to those contacts get pushed back to MobileMe and subsequently to your iPhone and other devices (including your Macs. 😉
There you have it. Sneaky, but it works. MobileMe meet Thunderbird.