It's a pity is took so long. My workflow is great now with LR, so unless the RAW conversion (pure image quality) isn't much better with C1 4.0 it's too late for me to change. Waiting for the first reviews. :)
I used the beta of 4.0 a few times. It seemed to do a competent job of converting some of the 5D raw files I fed to it (though not all). In a couple of cases I was seriously impressed by how well its default
conversion looked. But not all...
But there were irritating problems with the beta's UI. Judging by forum traffic on PhaseOne's site, long-time users of CaptureOne weren't universally thrilled by all the UI changes. I disliked the previous version's UI quite a bit. I'm not unhappy about the changes overall. But I could see from message threads in the forum that the company seemed to be on the verge of seriously irritating part of its established user base. During the short time that I participated in their forums, the PhaseOne people themselves were noticeable in their absence -- few company responses to the forum messages. It was hard to tell what weight, if any, they were giving to the end-user comments. (Absence of evidence ain't evidence of absence, but still...)
Some people who keep an eye on industry news -- I think Michael Reichmann might have been one of them -- have wondered "aloud" if the C1 update won't be too little, too late. I don't know the answer, but it's certainly true that they took a long time getting this update to market. In the meantime Lightroom seems to have become quite a bit more popular (its own UI quirks notwithstanding).
The last C1 v.4 beta I downloaded didn't have anything like the extensive HSL controls that are available in Lightroom, SilkyPix, and others. It had a somewhat crude drag-a-tiny-spot-around-a-color-wheel-with-the-mouse control. Even if the quality of its conversions turns out to be very good...once you've had a chance to work with the HSL controls in a converter, software lacking them seems...well, lacking.
One thing I noticed in C1's favor: excellent rendering of fine image detail. Well...I'll download the release version and hope for some significant UI improvements since the last beta version.
Given what C1 "pro" is liable to cost and given all the image-organizing tools available in Lightroom, I wonder how (if) C1 can steal some of Lightroom's (probably less expensive) thunder.