Happy, Happy, Joy, Joystick
Not only is this stick great for SF4, the buttons light up which helps when playing in a darkened room...its the shizz-nitt. I can't say anything bad about this stick...I put my Hori down once I got this joystick

Get the HRAP (Hori Real Aracade Pro/EX/etc) instead
I have 4 Hori joysticks, 2 of them being more or less clones of each other - this and the PS3 version (FS3). All use Hori Sanwa knockoff parts of the lowest degree. The PCB in this is also a bad violator, as it can cause lag and latency as pointed out earlier, or simply fail.
Buy at your own risk - this is not PlayAsia's fault and Hori can make excellent Joysticks. Just not this one. This is a cheap one that comes with very cheap components, and unless you are planning to do a full modification to the thing, not recommended as buttons will eventually fail, the joystick is garbage, and the PCB is as well.

Hands down my favourite stick.
I first fell in love with Hori when I bought two import Hori Arcade sticks for Dreamcast. After that I swear by them. I presently have two Hori sticks, and only prefer the 6 button layout. I still think it is a durable stick, (my Dreamcast arcade stick still works). I have been playing SFIV on my arcade pro, and find it responsive. I also really liked that this stick also works on your computer. Making MAME games super fun to play.

Also in reply to Boavista; playing this stick with Pacman CE, honestly the game is fast and nothing out there save for a 4 way really will make that game play any easier. (and I only play Pacman with arcade sticks)

No title
This fighting stick is certainly better than the 360 controller but is nothing when compared with the Real Arcade Pro Ex

Arcade at home
It's a good product...For fighting and shooting games,it's much more better than the classic pad.