DxO finally released their Mac version of DxO Optics Pro (version 5) as a beta. Link is: http://www.dxo.com/intl/photo/dxo_optics_pro/beta_mac
I've been trying the Windows release version on Win XP running in Fusion and while the user interface is a step down (IMHO) from Version 4.5, the results can be marginally better.
The Mac beta still has parts missing according to the read-me, but it seems capable of pulling a bit more detail out of Canon RAW images. And the UI looks cleaner than the Windows version. It's stable but, being a beta, a lot of things don't work; fortunately, it doesn't disable a V4 installation.
The beta is good through 6/15.
(I asked if he'd used the previous v4.5 for the Mac)
Yes, I've been using DxO since V4.0 was introduced, after using Bibble for years. One big advantage with both V4 and V5 is very effective compensation for lens deficiencies which are computed for each lens/camera combination at different focal lengths, focus distances and f stops. The compensations can be applied (or not) and the degree of application controlled. The advantages are especially notable at wide angles, which tends to add lots of distortion and vignetting.
For example, my Canon 24-105 f4 is remarkably sharp at 105mm on a 1DS2 (the vibration reduction helps a lot, too) but has a lot of chromatic aberration. I frankly didn't notice that until I processed some images in Bibble and saw the difference.
Since lens sharpness tends to decrease near the edge of the frame, more sharpening (specific to the lens and zoom) is added there to compensate, deceasing as you reach the center. You can also add your own level of unsharp mask, with adjustments similar to Photoshop.
The major differences between 4 & 5 that I've seen so far are the better interface in 4, smarter noise reduction in 5, and slightly better detail in 5, as long as you don't use the default settings. The color you see in V4 and the Windows version of 5 is what you get when processing is done; Mac V5 seems to give very washed out colors unless you crank up the Smart Vibrancy, which increases saturation but not on skin tones.
It will also use multiple processors and cores, one per image and runs very quickly on a Mac Pro, though that hasn't been implemented in the Mac 5 beta yet.
Be aware that it's heavily copy protected (the Interloc system)...
I will say that after months with Windows V5, I was going to just stay with V4, but the Mac beta is tempting me to upgrade once a final, complete version is released.