I can't give you an A/B comparison as I've never had a stand-alone BD player. I got a PS3 for the sole purpose of playing BD's. I never use it for gaming.
The one benefit I've heard about the PS3 over stand-alone's is it's quick load time. My guess is that newer generation stand-alone's have narrowed that gap, but I can't tell you for sure.
I can tell you that the PS3's software is elegant, intuitive, beautiful, and blazing fast.
Although my previous statements are not a testament to image quality, I can't see how anything could look any better than my PS3. This is using a 61" DLP TV at a viewing distance of about 9'.