Originally Posted by: Lao_Tzuwhy learn how to recognise intervals what can u do when youve learnt them?

Once you have a firm grasp of intervals you can play (mimic) anything you hear or anything you can think of immediately.

I did some tutorials on intervals here:
http://www.guitartricks.com/tutorial.php?input=362
http://www.guitartricks.com/tutorial.php?input=462

It also helps a great deal with improvisation. I recently did a tutorial on that here:
http://www.guitartricks.com/tutorial.php?input=483

Hope this helps.