The question about which is better, FW (400) or USB2, is not so easily answered. If you have a PPC Mac, or are not running Leopard, FireWire is definitely the better connector *on the Mac*. Reason being that you cannot boot a PPC Mac off a USB external hard disk, but you can with an Intel Mac...
If the leaked case images for the new laptops are real (and I believe they are), then not only will there be absolutely no Blu-Ray in a MBP (too thin), the MacBook appears to no longer have a FireWire port at all. This is just the next step in getting away from FW, I'm afraid. I personally...