First impressions are excellent: the card is very attractively packaged with a 'high-end' feel to it. The card itself is on a very high quality PCB substrate and clearly uses very high quality components.
Fitting into my case (a Silverstone HTPC case), the card could not be screwed down fully as the back panel is slightly too long at the bottom, and this would have caused misalignment of the PCI-E connector. Note that the card requires an additional IDE-style power connection, and won't work without it. The card is reasonably slim, but too high to fit a low profile case.
There is both a rear headphone output and a front panel headphone output as part of the HD-Audio interface (also line in and out on the rear). More on these later.
Getting the drivers to install was a pain: my brand new, clean Windows 7 64 bit installation wouldn't detect the hardware, and I needed to install the drivers myself. This turned out to require searching for the drivers on the supplied DVD-ROM as the auto-run file didn't work properly.
Once installed, my impressions of the software are not great. I have only managed to get ASIO sound operation working so far, and adjusting the volume is tricky for headphones. The software is 'skinned' to look like a cheap 1980s HiFi compo with lots of flashing lights and buttons, rather than making it easy to configure the things you need and otherwise staying out of the way. The Dolby virtual surround for headphones is fine if you have ever wondered what it would be like listening to music in a fishbowl, but otherwise it's total garbage. My card defaulted to Dolby Headphone enabled, which is definitely not what you want, so make sure you switch it off before doing any serious listening.
So far, so below average, to be honest. However...
Plug headphones into (HD 595s) the rear socket and play a couple of high quality (lossless) CD rips. All annoyance melts away. The sound is very good indeed, with excellent detail, separation and body. While it's too early to make detailed comparisons (and the headphones need a bit more 'running in'), the sound is certainly in the same ball park as my main system (Meridian CD 506, Cyrus Audio amp, ProAc speakers) and possibly better. Certainly like nothing I have ever heard coming out of a computer.
As a more concrete comparison, the same rip, via the same headphones on my iPod sounded far thinner and more constrained, so it is definitely a major step up from what is a pretty decent portable player headphone output. I am very impressed, and the proof is that I ended up listening to tracks for several hours before realising that it was 1:30am.
The front HD Audio headphone socket isn't in the same league, by the way - it was a little better than the iPod, but I won't be using it again, despite the convenience.
Very highly recommended if you have the time and technical expertise to configure it, and care about the sound enough to forgive the fiddling.