@Tiiki
Hit rating DOES provide burst damage. In fact, it's arguably just as effective as crit rating (if not moreso) for burst damage.
Consider that hit rating changes misses to hits, while crit rating changes hits to crits. With RED, Murder, and against 450 resilience, your white attacks will crit for about 1.62 times as much as a regular hit. This means that changing a miss to a hit adds as much damage as a regular hit deals, while changing a hit to a crit only adds 0.62 times as much, or less than 2/3 as much damage added. Replacing a miss with a hit is MORE effective at adding burst damage than replacing a hit with a crit. In addition, hit rating converts at a much more favorable rate (15.76 hit rating per 1% hit, versus 22.08 crit rating per 1% crit), so you're getting more of it. All said and done, hit rating adds more than double the white DPS as crit rating does.
The difference is that hit rating doesn't really benefit yellow damage as much (outside of frost mages, etc.). However, white damage is still a very large portion of your overall damage. This combined with the other utility advantages of hit rating (poison application, spell pushback, Blind not missing against ShS rogues, specials not missing against frost mages), I think hit rating is superior in almost all aspects to crit rating, point for point.
Now, don't get me wrong, I know you're talking about agility -- but I wanted to at least point out that hit rating does provide burst, and was using crit rating as my comparison. The added dodge and armor of agility help to make it more advantageous, but hit rating is still very, very good.
@ Jakani
In zero resilience situations, you'd be accurate. But resilience has a large effect against crit rating, a smaller effect on AP and agility, but -- here's the kicker -- ZERO effect on hit rating. Literally zero.
Hit rating isn't a better DPS increase than AP or agility, no, but it does provide other benefits (as listed above). I wouldn't take it in all my sockets, but I definitely take
[Glinting Pyrestone] over
[Wicked Pyrestone].
To me I would only consider gemming all hit rating if it would put me over 10% so I'll know I'll never miss against a frost mage, but it takes too much to get up there in full PVP gear. I definitely wouldn't complain about hit rating on PVE gear though, if I had any T6 to wear.