Many (most?) audio interfaces use FW (including mine). Many of us stayed away from the plastic macbooks due to graphics/performance. I was so pumped about the udpates...but no FW makes it a deal breaker for me.
These audio interfaces are expensive (almost the price of the plastic macbook in some cases), so it isn't as easy as 'go buy a USB version'.
Not to mention that many (most?) DV camcorders are FW only (you have to either go down in quality for USB or up in quality for quasi-HD (and up in price) to go USB).
I have to agree with many others complaining about no FW....seems they did that to force us up to the MBP. Strange that the lowest level laptop and the highest level laptop have FW, but none of the in-between models.
So, for many musicians/producers and many DV video users, these new macbooks are like salt in a wound...we finally get the updates we've been wanting, but now we can't use the machine.