gigabit is way faster then 100ethernet....still not as fast as FW but faster then USB1...i have a macbookpro and transfer reasonably fast...the best thing about the infant is the autoexpanding volume, so you can add drives as you grow, without having to re-format, re-save,.... also they work great as servers...ready michaels article on the infrant...
i also have a FW800 raid5 box, which is of course faster, but for storage i would get another infrant before anything else...they are simply way more versatile and the speed is acceptable...i think the new NV boxes are even faster...i have an x-raid...