I just used Migration Assistant a few days ago to transfer all the stuff I had on my old drive to my new 250GB drive.
It copied all the applications i'd installed, my custom color profile, and all by browser settings, cookies, and bookmarks, Mail accounts and settings, as well as all the files and folders I had on my desktop.
In fact, when I launched FireFox for the first time after 'migrating', it asked me if I wanted to pick up where I left off.. I clicked 'ok' and BLAM! I had the same pages up in the browser as I did before I shut down to install the new drive.
All in all, I was quite impressed. Everything was transferred over to the fresh install with the exception of:
Dock Icons:
I had several applications I use frequently in the dock. I had to put those back, and remove the ones I didn't want (iChat, iCal, etc).
Widgets:
Migration Assistant apparently does nothing with this.. so I had to go thru and close the Widgets I don't want that are there by default, as well as re-select my Zip code for things like the Weather and Yellow Pages widgets.
System Sounds:
Migration Assistant did NOT transfer the sounds i'd added, like the Wild Eep and Moof, so I had to put those back. Wild Eep has been a part of MacOS as long as I can remember.. it's sacrilege that it was dropped on OSX.