Yup. I have one. Use it with Cubase VST32 V5R6, to fly tracks up and down from my D1624. It was pretty easy and straightforward to set up, since I use the D1624 as the master word clock source for my whole rig (since it has the converters in it), and slave everything to it.
I very much like the Hammerfall: as advertised, the thing is absolutely dead-nuts bombproof (now that I have a semi-reliable Cubase, anyway...). Shoot, a few days ago I even tracked some stuff straight to Cubase, just using the D1624 in record-pause only as a converter box, instead of printing to its internal drive and flying down later. That was something I'd sworn that I'd never do...
I don't know of a user forum, but the RME website has a great deal of information:
http://www.rme-audio.com/english/index.htm
Although, perversely, that site now shows up as a 404. I suspect that that's just a temporary glitch, though- keep checking it over the coming days. Probably somebody just forgot to pay the registry fee...
If you're having problems, I'd bet a beer that it's probably with clock generation and sync. What's up?