when do you guys you kers on the track?

I don't think it does you any good while already on 7th gear (the gearbox will only let you go so fast). KERS was designed to aid accelerating out of slower corners - that's where those extra 80 horsepower make a difference.
IMO you should use it when leaving a corner leading to a straight, so you can reach your top speed sooner.

 

While watching the race from Singapore the weekend, I heard MB say that it's most effective between 3rd-5th gear... due to the acceleration boost obviously.

Anything below 3rd mainly causes wheelspin in game and anything above doesn't have a great advantage... Play around in practice and see where you feel most comfortable/fastest using it!

 

I use mine out of as many corners as i can. this gives me a better feel for where its really making a difference and often means i don't need to increase the fuel mixture and run the risk of running out of fuel.

 

The short answer is when you need it, every lap is different. Definitely as part of excelleration.

 

i only use Kers when im exiting very slow corners, medium and fast corners it's not needed, if however you don't use much kers up then just use it on the straight near the finish for whatever track, it's always better to use kers in each lap then not as it will benefit you.

 

This. Coming out of medium or low speed corners is when I usually hit it. If I'm fighting to defend a position, I try to save as much as possible for the DRS zone though. It doesn't increase your top speed but the extra acceleration can be the difference between retaining and losing the position.

 

Same...coming out of slow corners. I also sometimes use it in conjunction with DRS to pass someone, but still debating on how effective it actually is over just DRS alone.

 

I've found it to be a very effective combination. Reduced drag from DRS + 80bhp from KERS = insane acceleration usually.

 

I use it mainly out of slow corners once the car is straightened and accelerating eg. Sepang turns 4 and 9 (which are uphill too!), Monza after 1st chicane etc.

Also... other uses

In quali save one laps worth before attempting a hotlap, then use it all just before you cross start line, then you get a recharge for the rest of the lap.

I sometimes use it on the run-up to the DRS detection zone to try and get within 1 sec of car in front.
Combined with Mix 3, DRS for an overtake on a long straight, but watch out! The braking zone gets much longer if your 350KPH+

 

I find myself in qually using it usually in the low rev range of 5th and 6th, little squirts to get to the higher rev range of those gears quicker, in a race I'm either using it to defend in the DRS zones or using to get into range of the DRS zone. If I'm neither attacking or defending I revert to using it like I do in qually.