I have seen it drop off sometimes and not other times. Warriors,Paladins, and DK's have a similar attack speed debuff. I think it has to do with who put the debuff up first. Either way, the talent IMO is worth it because Blizz balanced the bosses with the thought process that they would have their attack speed lowered by 20%.
In some cases, you might not have any of those classes available to use that debuff on your target(Offtanking another mob, DC'd, just simply not available to your raid), therefore you're taking more damage because you don't have it yourself.
I don't really have anywhere to put those points that I find it really important to drop this in favor of. Sure, I could dps a little better if I moved those 3 points into something more kitty related, but I would rather tank anyway. If I'm dpsing, it's only cause us ferals are just that good :P