I have put about 6 days on these with a K2 parkstar. I am very confident and comfortable in them. Fairly flexy for park and responsive enough to bomb. I do have some gripes though. The highback adjustment on the back comes undone and slides up, allowing the highback to pivot further back than my boot will go. I had to cinch it tighter with an allen wrench to get it to stay, which makes it difficult to adjust later. The ratchets work well but if you pull the ratchet all the way back when tightening, it can get caught up on the release tab so it doesn't fold back down flat. Lastly I stepped on the highback getting in line for a lift and bent it severely sideways and heard a 'pop' - I thought I had broken it. Fortunately the highback seems to be functionally fine, a large portion of the paint/clearcoat had cracked and peeled away. So half of that highback is matte black while the rest is shiny. It has started peeling in other areas too, like the high flex area around the bolts where the highbacks connect. So all in all a great performing binding so far, with a few QC issues that can be fixed or are cosmetic. Definitely worth the $$ if you buy in the sierra board package deal.
I have put about 15 days on these bindings with an 08 sierra crew. Total time has been about 15% park, 20% tree runs, 30% powder, 35% groomers. This binding does everything I need it to, it's great for beginners to intermediate skill levels like me. Responsive and reliable, love the toe cap. I will be getting a more park oriented binding this year but the doom will stay in my arsenal for cruising days.