I know this article is about the desktop APUs, but as I've been running the C-50 Ontario on my netbook (Acer AO522-BZ897) for a few months now, I think I can share some real-world experience.
Overall: It's a dual-core netbook, and still gets 6 hours battery life if I'm writing code with the brightness down, a little less if I'm listening to music. It may be slower on the individual cores than a competitive Atom, but if your program is threaded it's great. I'm very happy with the performance. It replaced a Powerbook G4 (I know, different class altogether, but still), and in terms of % CPU used for common tasks it's far and away better. No more mp3/m4a decoder taking 10+% CPU for decent bitrate songs.
Real-world Performance: I can say that any downside I've seen is entirely due to bad software - I hear that in windows I could watch 720p on it, but right now with x64 linux and the beta multi-threaded flash player in the latest firefox or chromium I can't watch youtube videos at more than 480 before it starts to drop frames. Not a big deal for me though. Once the video drivers caught up with the chipset I can say that compositing and desktop effects work flawlessly, no lag whatsoever. I don't play games on it, being a netbook, except for the occasional flash thing (which sometimes lag, but again that's the flash plugin).
Hooking it up to a 1080p TV over HDMI and running at native resolution, playing standard definition (624x352) XviD files zoomed to fullscreen works flawlessly in VLC. 720p x264 almost works - it saturates a single core and drops a frame here and there, and will really hang if you try to bring up a semi-transparent control bar over the video, but again if the codec were multithreaded it would be perfectly fine. I suspect that VLC on linux isn't taking full advantage of the GPU here either, considering I'm running the open source radeon drivers and not the official binary. For those of you running with officially supported closed-source software, i.e. official drivers or windows, I suspect it might even play 1080p without a problem.
Let's remember that this APU is in the same power class as an Atom, and it's a netbook - impressive performance in my mind.
As my only direct comparison points are the G4 powerbook that it replaced and my Phenom X4 9950 desktop, it's (gasp) right in the middle, but comparing a netbook to a desktop built for CAD and gaming is stupid, and so is comparing it to something 5 years older.
My only gripe is that you can't set how much RAM the GPU side takes, so no matter what size stick I've got in there the system sees the total minus 256M. The upside is that you only need a total of one stick of RAM, but the downside is that when it comes with a 1GB stick, suddenly you're trying to run a windows 7 system (out of the box) with ~750MB, and that's asking for trouble. As I swapped out the HD and RAM before ever turning it on the first time and installed linux fresh, I can't say I've seen the slowdown, but it could be there.