I got my new iMac yesterday and decided to try out Migration Assistant since it got mixed reviews on the places I checked. My experience with it wasn't so great. 
First, I'm migrating from a G4 to an Intel processor. From what I've read you don't just want to migrate everything over because of the different architectures and some older apps can actually cause the Intel machines to malfunction. You can have Migration Assistant not migrate your apps (only choose settings and/or data). But, I still ran into a problem.
Apparently, there were a couple of iTunes files (songs) that would not come across the Firewire (for God knows what reason). But, the result is my migration would run for hours, then just hang. I tried it several times. Migration Assistant gives NO feedback as to what the problem is. Then, I decided to try this the manual way (which is when I discovered what the problem files were). Everything was migrating fine until I tried to migrate over my iTunes library. Narrowing it down, I found out that 2 of the almost 3,000 songs in my library were the problem. Even trying to pull them over using the Firewire target mode, the migration would work until it got to these songs, then just hang. I figured out which songs were the problem by going to the new library and looking at the last artist folder that migrated over successfully. The next folder was the problem. So, if you're using Migration Assistant and running into a mysterious problem, this could be it.
I found this article in Apple's Support Forums to be very useful:
http://discussions.apple.com/thread.jspa?threadID=435350
Some other tips. I found the easiest way to migrate iCal, Address Book, SOHO Notes and Mail were to use the sync function of .Mac. I reset the sync data overwriting the .Mac account with the stuff off my old machine (I have a laptop that I sync also). Then, I went to the new machine and reset the sync data doing the opposite (overwriting the data on the new machine with the .Mac data). This worked like a charm.
Actually, I'm still in the migration process. I had a slight hiccup with Chronos Notes but got that figured out (threw away the preferences on the new machine and it started showing all my notes again). This is taking longer than Migration Assistant would have. I still have a ton of apps to reinstall. So, I'm sure I'll run into a few more things. But, I feel like I'm getting a cleaner install than bringing over almost 5 years worth of stuff that had accumulated on my G4.
Hope this helps someone.
Peace,
Brian
First, I'm migrating from a G4 to an Intel processor. From what I've read you don't just want to migrate everything over because of the different architectures and some older apps can actually cause the Intel machines to malfunction. You can have Migration Assistant not migrate your apps (only choose settings and/or data). But, I still ran into a problem.
Apparently, there were a couple of iTunes files (songs) that would not come across the Firewire (for God knows what reason). But, the result is my migration would run for hours, then just hang. I tried it several times. Migration Assistant gives NO feedback as to what the problem is. Then, I decided to try this the manual way (which is when I discovered what the problem files were). Everything was migrating fine until I tried to migrate over my iTunes library. Narrowing it down, I found out that 2 of the almost 3,000 songs in my library were the problem. Even trying to pull them over using the Firewire target mode, the migration would work until it got to these songs, then just hang. I figured out which songs were the problem by going to the new library and looking at the last artist folder that migrated over successfully. The next folder was the problem. So, if you're using Migration Assistant and running into a mysterious problem, this could be it.
I found this article in Apple's Support Forums to be very useful:
http://discussions.apple.com/thread.jspa?threadID=435350
Some other tips. I found the easiest way to migrate iCal, Address Book, SOHO Notes and Mail were to use the sync function of .Mac. I reset the sync data overwriting the .Mac account with the stuff off my old machine (I have a laptop that I sync also). Then, I went to the new machine and reset the sync data doing the opposite (overwriting the data on the new machine with the .Mac data). This worked like a charm.
Actually, I'm still in the migration process. I had a slight hiccup with Chronos Notes but got that figured out (threw away the preferences on the new machine and it started showing all my notes again). This is taking longer than Migration Assistant would have. I still have a ton of apps to reinstall. So, I'm sure I'll run into a few more things. But, I feel like I'm getting a cleaner install than bringing over almost 5 years worth of stuff that had accumulated on my G4.
Hope this helps someone.
Peace,
Brian