OK- So I'm totally late to this thread... but Raw processing is my full time business. I started out using Capture One when Photoshop was still simply "CS."
I liked C1, but it took me a little while to get used to it.
Pros: background processing was implemented well.
Cons: It wasn't as intuitive and fast as I hoped and it left a trail of messy folders, subfolders and working files.
Then I moved on to Bibble... Just not fast or user friendly. Bought the app, used it for a few thousand images, hated it, wish I could have got my money back. :(
Once CS2 came out and ACR was pumped with steroids, I gave it a go and never looked back. I love its integration with Bridge and the whole suite. It's got plenty of horsepower and speed!
I started my own post production company and our business runs IS Raw processing. Though Aperture and Capture One are amazing products, I couldn't imagine trying to run through the volume with any other app.