Firewire 800 is way, way faster than USB. If you have a FW800 port (pc or mac, doesn't matter) and you are buying an external HDD, get one with FW800. It's still slower than esata but unless you have a mac pro/macbook pro you won't have the option.
About the updates... honestly they are meh-worthy:
a) crippled 4-core mac-pro; unlike previous iterations they are skimping hardcore on this one - the motherboard/processor combo it uses can't accomodate a second processor down the line so you are stuck quadcore, forever. Maximum amount of RAM has been crippled compared to the octocore. In a nutshell? the quad-core macpro is really cheap to make this year but zero savings have been passed down to the consumer. The nehalem inside the 4-core mac-pro is just your garden variety nehalem (ok, supports EEC ram whatever) and it's really cheap compared to the server grade "true" xeons used on the octocore.
b) imacs: no LED displays, no quadcore core 2 duo/nehalem (god forbids someone buys an imac instead of a macpro...). Basically last year machine, just a few more megahertz, ram. Ah, the vidcard is a rebadged nvidia, performance improvements compared to last gen are slim in the graphical area, unless you splurge and order one with the 4850. Which by the way, they dont let you do neither on the entry-lev
el 20 incher nor the cheapest 24 incher. How sweet of you, Apple. Also, unless you bother to tick the proper checkbox, imacs come with a gimped keyboard missing the numeric keypad (and extra function keys) on the right.
c) mac mini: stuck with a 2.0ghz core 2 duo (god forbids someone buys a mini instead of an imac...). Ah, the RAM is painful to upgrade (requires full disassembly) and they charge you an arm and a leg for the extra gb of ram on the 2gb mini. But hey, good news here: dual display support out of the box and FW800 instead of FW400.
Ah, if you live anywhere but in the USA, boo-yaa! price spikes for everyone. Enjoy.
The only good thing that came from this update is the mini and the option for sort-of-nice ATI cards if you are willing to spend the extra money.