Is Jump Shoot Jump a Worthwhile Mechanic?

I'm on the fence about this one because I have not played many games against units which have a JSJ mechanic (I don't know if I've ever actually played Tau - ). I have heard that facing units with the mechanic can be annoying. What have been your experiences facing units with the JSJ mechanic and do you think that it is too frustrating to be considered a viable mechanic to exist in the game or do you think that given a fair points cost for such a powerful ability that it would be fine to occasionally crop up? A big thanks to Dr. U. R. Ian Rakarth for the complementary therapy session after the discussion!

People who complain about it don't know how to position themselves. Tau doing it doesn't bother me since it is the only thing that gives their suits any mobility, and even then it's rarely more than 12" per turn. Eldar doing it isn't a travesty either since their units can already go wherever the hell they want in a single turn. It also tremendously benefits armies like Corsairs which are built entirely around being able to do that.

{strokes beard thoughtfully}  I see what you're saying.  How would one counter such tactics?  I find a good way to check balance of a rule is to see whether or not there is a clear, viable counter-measure.

I think that it depends a lot on the table. If there is a lot of LoSB terrain the rule is insane. And the only tactic against it is having enough guys to herd them (not always easy against for instance eldar) or having the speed to engage them anyway.
Usually having high speed yourself, just raw numbers, or a targeting mechanism that does not need LoS are the best counter tactics.