Anywhere. Honestly, there's nothing special about so-called "Mac" drives, except for the packaging and maybe some Mac specific software bundled with. The hardware itself is completely indistinguishable from the non-Mac version.
As for what you lose out on with Firewire... Not a whole lot honestly, but FireWire is better for moving large files or even large numbers of files. Primarily because it has its own dedicated controller chip, whereas USB uses the main CPU. However, for probably 99% or more of people, there's really no difference between FireWire and USB 2.0 since you don't have a PPC Mac (which could only boot off of Firewire drives).
I'm personally not familiar with this GoFlex thing, but I'd be pretty leery of it myself. If you need interoperability with Windows, look into FAT32 or ExFAT (sometimes known as FAT64). I personally wouldn't go entrusting any kind of important data to some kind of overlay software that came bundled with a HDD. At least not when there were perfectly workable alternatives with native support in both operating systems.
Hi all,
It's black friday and I am looking to get a deal on an external HDD for use with my macbook pro 2010 13 in model.
Can someone suggest a website where I can get really good deals on a 500 to 750 GB drive?
Also, if I just go for the usual USB drive instead of a Firewire equipped one, what do I stand to lose out?
Finally, I came across a GoFlex technology by Seagate which allows for the drive to be used with both Windows and Mac OS. Is it a good idea to go for this? Could it create compatibility problems of any kind, especially if it's still new?
Thanks!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic