If you are going to take this stuff seriously, you really need one (A good stick, custom if you are rich or clever enough). The 360's analogue is fine for inputs being so nice and smooth, but the buttons on a pad, any pad, just do no cut it for the combos you need to pull off in anything other than casual play.
I'm never going to be good enough to warrant the $150 stick. While using it on the PC makes it a very great temptation, I don't think I'd get my money's worth out of it. Still sorely tempted, though. Especially at importing a stick from Japan, since didn't Hori have the rights there?
Was going to buy the Hori EX2 for 360 (I want a headset port if I'm playing it on the 360) but they were sold out everywhere nearby.