Time zone

Forget about counting every single repetition. Instead grab a stop watch and go until your time is up. Trust me, you will not anticipate working this hard.
Here is the problem with counting repetitions. We naturally tend to anticipate what's next and in turn trigger out bodies to work at specific rates. Take for instance, you are performing squats for 20 repetitions. You will 9 times out of 10 make your body start at a slow and comfortable rate in order to save enough energy to finish the set.

By using your stop watch you have no idea when to stop. Your just waiting and praying for the clock to beep so that you can rest. 
Next time your at the gym or at home give it a try.

Sample routine ( use weight 50% max):

Db jump squats 3x30 sec
Db isolation lunges 2x60 sec
Db shoulder press standing 4x20 sec
BREAK
Db seated hammer curl 3x30 sec
Db standing upright row 2x60 sec
Db chest press 4x30 sec
BREAK
Db walking lunges 3x45 sec
Db flys 2x45 sec
Db seated row 4x20 sec

Have fun