lot of rogues concern themselves way too much with their level of hit rating. I'm going to try and consolidate all the information I have about it in this post.
Contrary to popular belief, there is no "magic" number for hit rating. There is an absolute minimum, and "cap". Well, really there are two caps, but I'll go into that later.
The hit caps are as follows (assuming 5/5 precision):
Special attacks: 64
Auto-attacks: 363
Therefore, the minimum amount of hit for a raiding rogue is 64, which as you probably know, is so easy to get it's barely worth mentioning.
Between 64 and the cap, hit rating is simply another linearly increasing stat.
But if hit rating is not important, why gem it over anything else?
Hit, while not the be-all-and-end-all of rogue dps, is the highest "bang for your buck" stat out there. Meaning that 1 point of hit rating will give more overall dps than 1 point of agility/ap/younameit. Therefore, a +8 hit gem in a socket will outweigh +8 agi (exluding socket bonuses).
Beyond the 2 purple gems required for your meta, every socket where the bonus is shitty should contain a yellow, hit rating gem. I'll leave the determination of worthy socket bonuses for another day.
Is there a point at which I should stop gemming for hit?
Yes, at the cap. However, as I touched upon before, there are two caps. The hard cap at 363, and a soft cap at approximately 296. This soft cap is determined by subtracting the effects of Spicy Hot Talbuk (the food of choice) and Improved Faerie Fire from the hard cap.
Since we generally have a raiding moonkin, I personally would be inclined to start substituting +hit gems for +hit/+agi at around this soft cap. But you may like to sub items in and out depending on the moonkin attendance.
Conclusion:
Hit is cool. Hit is not important. Never take an item just because you believe you "need" the hit rating. If an item is a dps upgrade, wear it.
i myself did not write this but a guildie wrote this and we did some testing together, i do not expect any rep since i did not write this guide.