I recently switched over to Photoshop CS5 from CS3 and did a quick test of the new raw processing engine (Adobe Camera Raw 6.0).  To say I was impressed is an understatement.  Here's a sample image processed with default settings in CS5 (ACR 6.0), with a CS3 (ACR 4.5) version supplied for comparison purposes. This image of Sydney musician Justine Wahlin was taken in fairly low light on my Canon G9, exposure was 1/10 at F2.8 and 800 ISO.

The differences between the converters are fairly subtle at such small sizes though you can already see some breakup and colour noise in the floorboards of the CS3 processed version.

See below where I've included 3 different sections at 100% to show how each converter deals with skin, fine texture and shadow areas.

At 100% it's obvious how ACR 6.0 has totally removed the blotchy colour noise present in the CS3 version.  It also has a very tight and in my opinion much more filmic grain pattern.  The skin tones are much cleaner and would be unoffensive even in a decent sized print, especially in comparison to the ACR 4.5 version.

This section shows that we are not losing any fine detail to gain the much improved noise performance.  The much lower chroma noise even enhances the apparent detail in the fine flyaway hairs to provide a more realistic rendition.

This out of focus shadow area again shows the cleaner results, tighter grain structure, and smoother tonal transitions provided by the new raw engine.

I've usually considered 800 ISO to be a bit of a last resort on my G9, yet now I'm keen to try 1600!  I'm also looking forward to running some of my 6400 ISO Canon 5D mkII images through ACR 6.0 to see just how much more usable the resulting images will be.  All in all a very impressive result that bodes very well for Lightroom 3.0, as they share the same new conversion engine.  In the past I've felt that though I love Lightroom for it's speed, features and file management I always knew that I was not really getting the best absolute pixel level quality from my files.  That has surely changed with this latest release of ACR and Lightroom. Nice one Adobe!