I actually carry two of these, as a backup. Some people need 1 for the old, one for the new and you can just copy between the two. Takes FOREVER if you're attempting to do a large drive with MP3's, etc though.
The last HHD I had to use this on was my wife's computer a week ago. She ended up getting a new 500GB drive and it took about 45 mins to select and back everything up to the new drive (she keeps EVERYTHING in her profile, so it was easy - if that had been my laptop, it would have taken all day). Then, I spent another 20 minutes fighting with Windows 7 since I was too lazy to set things up right the first time. At least it was my wife and not a customer... Live and learn.