What makes the JCW airbox so special?
Can you post up some pics of the insides and inlets?

 

It's special because it says JCW on it!

Real OEM might have some diagrams for you to compare. I've only seen pics like this one:
http://www.outmotoring.com/mini-coop...n2_intake.html

 

I has an expensive cone filter inside and a flap that opens at about 4500 rpm which allows more air into the engine. The flap closes when the rpm dips below 4000rpm. It stays quiet below 4500 rpm and starts to scream pretty loud afterwards. word of advise if you want to get it is do without the paper filter replace it with a foam or a cotton mesh filter. They cost way less and are both re-usable. Now the question will be which type will be better? Well you will have to read up on the older posts.
Cheers,

 

so its pretty much a flap, a hole, and a larger filter?

 

That link seems to be for the r56 intake, not the R53.

Here's a pic of the R53 JCW kit:

http://im1.shutterfly.com/media/47a1...D720/ry%3D480/

These and Dinan are said to be about tops performance-wise, but as I understand it the difference between CAIs is generally pretty marginal.

I had my sights set on a JCW intake for a while, but ended up going with the "Dave.F" modified stock airbox which tests even better than JCW (*) and is quite a bit less expensive.

(* = if anyone cares, I can try to get the exact citations from Minitorque.)