I got my bag from Muji.
Lovely clean black design, suitable for work or attending informal events. Can transform into rucksack design or messenger bag or brief case. All the bits tuck away and vanish when you don't need them.
Most laptop bags I've seen are quite cluttered in their design. This one isn't.
The Muji has a laptop sleeve inside, makes it really easy to pull my PB out and slide it back in.
The one I brought, last year's model, fitted 15'' laptops, but the internal sleeve was a tiny bit too narrow for my PB15 which has a widescreen. So I cut the sleeve down one side and hemmed up the edge, and it fits perfectly now.
Hopefully this year's sleeve will be wider to fit 15'' MBP. It already fits standard MacBooks and iBooks anyway.