To be useful this would need an eSata port. USB or even FW800 cannot be utilized for a practical external storage solution. The speed offered by those interfaces are excruciatingly slow to be usable, except maybe for timemachine which doesn't require the speed anyways.
Ok, let's be reasonable here--to be useful for
things that require massive data throughput. Sure, if I'm doing uncompressed capture to an 8-drive RAID array, FW800 is slow. But for many perfectly reasonable uses of a computer like this it's sufficient. 3D rendering, for example, could care less about disk throughput. Same with many kinds of video encode.
For the target audience--prosumer/low-end pro, it's perfectly fine, as many of those people just aren't running massive RAID arrays.
I managed to talk my wife into one as it's the first iMac that convinced me to replace my old pro tower rather than holding out for being able to afford a Mac Pro, and while I'd LIKE very much to see eSATA on it, I don't care that much in the near-to-medium term, since I keep all my data on a server connected via gigabit ethernet anyway, for connivence's sake. The internal drive is sufficient for the few things I need better speed than that on, and FW800 would handle a single-drive external case well enough, which is all I expect to personally ever use it with.
By the time I'm replacing it in 2011 I expect to see USB3 or other technologies available.
Really, there are people who have medium-to-high CPU needs who just don't need 300MB/s throughput to external storage.
