Does tea have more caffeine the longer it's brewed?

I know that the longer you brew it the stronger it is. Now whether that means its more caffinated or not I’m not sure. Sorry!!

There’s only so much caffeine in the tea leaves to begin with, and most of the caffeine is released early on in the steeping. So the answer is, technically, yes, but only up to a point.

(One of the ways of making decaffeinated tea is to rinse the leaves in boiling water before actually brewing the tea – this gets rid of a significant quantity of the caffeine, but alters the taste of the tea.)

It’s about the other stuff in tea. It changes the way caffeine is handled by the human body. If tea is brewed longer the effect of the caffeine is slowed down.

80–90% of the cafeinne is released in the first 30 seconds of brewing, so a long brewing time releases only marginally more cafeinne.

This really depends on what type of tea is brewed, how much is brewed, temperature, yadda yada.
http://en.wikipedia.org/wiki/Tea#Preparation