Man, I thought I was the only one in the lower 48 so passionate about riding to Alaska! I've done the homework and am hoping to go next year (after I get the hitch, trailer, and the S.O. to come along).
This is a good article to start with:
of course, that was 1999, so things may have changed quite a bit.
I had never heard of Milepost.com before this thread, but I will certainly be on that site quite often now that I do.
It would be really nice to rent a bike there and ride from Juneau to Anchorage (part of the way by ferry), then through Denali, and end at Fairbanks. The only bikes I could find for rent are the F650's, and I DON'T want to do that sort of mileage with any bike besides my LT, especially those Enduros, and especially with a passenger. If you find a good transfer company that can truck your bike there for you to ride home, let me know as I'm interested in that idea too.
The one thing I recall as the most challenging parts are the weather (if you get in a storm, which is very likely), the road condition (part gravel, part construction, all not-motorcycle-friendly), and the animals... how dare those Moose and Bears not yield to us humans on bikes!
With a trailer, iPod, rain gear, all our belongings, and most importantly my LT, I think it would be the best ride in the world.
But no, I haven't done it, I can only forward the info I've found. Hopefully someone on here can tell us what it's really like.