Some amount of haste will be vital. Generally, we won't be able to generate enough rage for all our abilities without haste, from both gear and the 10% melee haste raid buff. Like most stats, it plays well with others - obviously synergy with crit, but also with mastery as it increases uptime for Enrage for fury warriors, it increases the number of Strikes of Opportunity an Arms warrior gets. The interactions are actually pretty involved, with more haste leading to more Colossus Smash uptime, but negatively effecting Slam (since 0.5 seconds of lost attack time constitutes a larger amount of white damage).

However, once we have some sufficient amount of rage (not quite a hard-cap on rage), it's pretty clearly the worst stat for warriors. It'll only benefit white swings (and Strikes of Opportunity), so probably only 25% of the damage of a rage-capped warrior.

The caveat, the big caveat, is that the exact amount of haste needed to ragecap is uncertain, considering that raid damage contribute rage, and much debate rolls on about the best ratio of haste to crit/mastery. Once Inner Fury shows up, it'll be practically impossible to rage cap, but even then, it won't necessarily be the biggest dps increase on a per-point basis. My fury warrior seems to be having good results keeping mastery at baseline and having twice as much crit as haste, while maintaining hit/expertise cap, but that's just anecdotal. I can't definitively say that my 20% haste, 40% crit is any better or worse than 15% haste, 44% crit or 25% haste, 36% crit.