I'm a LFR-hero type casual, but I still try to get a good balance or priority of stats, which since launch has been Haste/Crit. I've recently seen well-known Rets going high Crit/Mastery, and letting Haste tumble down to the 18-20% range.
I've messed around with the gear I have a little bit to adjust
my stats accordingly, but I've found that Haste that low makes the spec feel awful to me. Maybe the reason for this stat priority is to set up the big, hard hit, or an attempt to avoid the wasted GCDs when Crusade and Lust are going at the same time?
After testing things out, anything less than 26-27% Haste just makes combat unpleasant for me.