I've been using it for quite some time now with a sennheiser hd598, for gaming exclusively, and it was really an enjoyable experience so far.
I own a xonar phoebus and the card's effects just don't cut it (a disappointement for a gaming sound card, the sound is good however). Xear surround headphones gives adequate positionnal audio, but it sounds really terrible. DHT is a false surround emulation since it's not detected as a 5.1/7.1 setup by games which autodetect audio settings (more and more common now), and sounds tinny/plastic with games that let you choose the audio setup.
So when someone suggested i try the razer software i jumped on the occasion, it was free after all. Sound wise, there's a slight dip in quality (with all audio "enhancements" such as bass boost, volume leveler etc... disabled), but not as bad as with xear and no plastic feeling, so i'd say it's acceptable. After calibration and a lot of adjustements i found the sweetspot that works for my ears and it works great i would say. The positional clues are spot on and the slight quality loss is not problematic in games, the added atmosphere compensates for it. In FarCry3 for example, with DHT aside from left/righ separation EVERY sound feels like it's just in your face and in front of you, there's no way to determine if something is coming from behind. With razer software it gets way better.
On the annoying side, most of the time i have to fiddle with the software when i want to enable it (i don't use it for music). The common problem is the cracking noise between channel changes. I've discovered that when you change outputs a few times in razer software's control pannel, with the effect enabled, the cracking disappears completely.