I am currently working with Capture One LE, and I basically like the results. Its main downsides are that it is agonizingly slow on my MacBook, that it is not possible to develop several images with the same setting at once (i.e. you have to process every image separately). I now consider buying a MacBook Pro and thereby change to Aperture, which, judging from what I have heard so far, seems to be a good piece of software. What attracts me most is its photo management tool as well as its quick-fix tools.
I would be interested in hearing about experiences with this software, as well as with other RAW-converters like Adobe Lightroom and OxO Optics Pro.