As far as I know, there are a few mates of mine who know this trick, but I'm not too sure if it's widely known by other hunters.
It's a pretty simple little macro that allows you to blow up mobs without wasting too much mana and hence generating downtime. Then again you can just use this trick with Aspect of the Vyper on and you'll be full on mana in no time.
REQUIRMENTS
To do this little macro you will need these two abilities at least.
-Steady Shot
-Kill command
enter the macro screen and type in
/cast Auto Shot
/cast Steady Shot
/cast Kill Command
Drag the icon down into a place of your interface that you wont ever really use. Now get that icon's hotkey, go into your key bindings and change that icon's hotkey to mousewheel up.
Now, when you click on a mob, pop your mark and sting, send your pet in to attack, then sit back scrolling up, as every click of your mousewheel will cast this macro. Please note that this can and will generate threat relatively fast.
This macro is only the basic macro that can be used, and has a lot of space for customization, however, keep in mind how much mana will be used by the abilities being continuously casted. In between, you can stop scrolling up and pop off an arcane or multi shot or renew a sting.
I do not claim that this is the best DPS strategy for hunters, in factI know that it is hardly the best. All it is, is a quick trick to help farm or grind, with little to no downtime.
Cheers.