Even though the PC version was delayed to September, the PC demo is available to download.

http://neocrisis.com/news/135-game-news/3373-batman-arkham-asylum-pc-demo-out-now

Minimum System Requirements
OS: Windows XP/Vista
Processor: Pentium 4 @ 3 GHz/AMD Athlon64 3000+
Memory: 1 GB
Hard Drive: 9 GB Free
Video Memory: 256 (nVidia GeForce 6600/ATI Radeon X1300)
Sound Card: DirectX Compatible
DirectX: 9.0c
Keyboard & Mouse
DVD Rom Drive

Recommended System Requirements
OS: Windows XP/Vista
Processor: Pentium D @ 3 GHz/AMD Athlon64 X2 3800+
Memory: 2 GB
Hard Drive: 9 GB Free
Video Memory: 512 MB (nVidia GeForce 7900 GT)
Sound Card: DirectX Compatible
DirectX: 9.0c or 10
Keyboard & Mouse
DVD Rom Drive

Requirements found here.

I don't currently have FRAPS installed so I don't have any hard numbers for my frame rate, but I just ran the demo and it performed well.

Here are the settings I ran it at,

1152x864
V-sync on
nvidia multi-sample AA - off
Detail level (governs 7 on/off settings) - Very high
Physx - Normal

Overall it looked like it ran well enough. I did have one or two spots where I could see some slowdown, but other than that it was fine. Unless I missed the key binding, the camera length behind you is a little too close and it's made worse that I'm not running a widescreen monitor so it feels like the sides of my viewing angle is further restricted.

As for controls, it'll probably take a few more times through to get used to them, but they weren't bad. I would like to use a controller, but the demo is set up to use the 360 controller and even with my PS3 controller set up, it wouldn't recognize it. Still, using the mouse to look around and right/left clicking for combat isn't bad.

Doesn't seem like a bad game, but I think I'd rather just rent it for the PS3 rather than spend $50.