I've been following it a few years as they've been killing it on Apple hardware... I signed onto the beta when they announced for Windows, which was a year or so back? I bought my official keys about 6 months ago when they ran a sale.
I think for painting, the brush engine is not there yet for Windows as there's optimization issues there, so Photoshop/etc is still needed.. but for vector work/photo editing, it's fantastic... I can't quit Adobe as it's still standard, but I think eventually they may give them a run for their money... I have Lynda and they have courses up there for the professionals, so I think at least right now photographers are seeing reason to switch over... and obviously being able to drop the subscription is nice