I did exactly what the OP is asking about. I used Migration Assistant to migrate the Time Machine backup of my 2007 MBP to my new MBA from a Time Capsule. I simply made an Ethernet connection between the MBA and the Time Capsule, started Migration Assistant and went to bed. The next morning everything that had been on the MBP was on the MBA.
As other posters have noted, migrating a backup over Ethernet takes several hours but it certainly isn't very hard to do.