When I think of all the time and money I spent setting up new computers - or fresh installs of the os in windows it makes me sick.
It's even better if you are migrating from a Thunderbolt or Firewire-equipped Mac to another Thunderbolt or Firewire-equipped Mac. Just connect the two computers together, and boot the old one into Target Disk Mode (reboot it and hold down the T key throughout the process). Your new Mac will see your old Mac as a hard drive. You can then run Migration Assistant from under the Utilities folder in the Applications folder. I migrated from my 2011 to my 2012 MacBook Air in about 20 minutes.
Migrating a Boot Camp partition is a little trickier. You can download a program called Winclone for $20. It will back up your partition onto a large file, which you can then restore onto a new Mac. However, sometimes when migrating to a different type of Mac things don't work correctly. For example, when I migrated my Boot Camp partition from my 2011 to my 2012 MacBook Air, the Boot Camp partition wouldn't recognize the keyboard and trackpad. I had to plug in a USB keyboard and mouse, manually uninstall the old Boot Camp drivers, install the new Boot Camp drivers, and search for hardware using control panel (and of course re-activate, having to use the phone option since I had already activated it on my 2011). It was still a lot easier than having to install everything again, however.