Some great insight on why linux isn't as popular as it should be, by Asa Dotzler of Mozilla Firefox fame.
The first issue, migration, is pretty serious. For "Regular People" to adopt Linux (which usually means leaving Windows) Linux is going to need a serious migration plan. . . . When Regular People fire up the Linux desktop for the first time, the browser, office suite, email client, IM client, file manager, etc, each need to carry over as much as possible of the Windows application settings and all or very nearly all of the user data.This has been one of my biggest headaches. I dual boot Ubuntu and WinXP, and I've set up FAT partitions that allow me to share most of my data. However, program settings, bookmarks, and browser history are just a few of the things that won't share across both environments. Setup was a pain in my the ass initially, and I questioned a few times why I was even investing the time. A serious migration plan would be incredible.
Of all the distros out there, I'm betting that Ubuntu will be the first to attack this problem. Their motto is "Linux for Human Beings" and thus far, they're doing a good job. With a major release every 6 months, I expect to see this distro become huge by version 10 or so. An MS slayer? Maybe not. But certainly a way to make inroads to people and show them the value of free software (free as in speech, and free as in beer).