After my experiences of the last few days I have to share the fact that in my opinion having an external hard drive and using time machine is an essential thing to do. 2 days ago I was burgled, they took my beloved uMBP and our Sony Vaio along with 3 PS3's and various other valuables. I have insurance who have agreed to pay out already so I replaced the uMBP yesterday. Fortunately they left my WD external drive. I unboxed the MB, chose the language and keyboard options on startup and then used Migration Assistant. It took about 2 hours but when done my new laptop looked exactly like the old 1, all my photos, music, work for university and everything else where exactly as before. Well done Apple for this simple but essential bit of software, it has saved me days and days of work.