So, I have an audio track going to a Bus that has an insert effect. I create a send level envelope on the audio track to fade in an out of the effect, however it does not seem to make a difference (well marginal at best) the effect is always there instead of only being heard when the level send is increased. I'm doing something wrong, I jsut can't figure it haha!

"an audio track going to a Bus..."
You don't have the Audio Track output going to the bus as well, do you?  The output should go to a Master Bus, and so should the FX Bus.  Set the effect to 100% wet, and you should hear the difference when you raise and lower the Send Level. 

^^^^^^^^
 
The track's output bus should be different than the track's send bus, one for the pure track output and one to balance/blend whatever plugin was added to that send bus.
 

ahh, okay thanks - I'll give that a go. First time I've tried efx bus (I noramlly just stick them all in tracks), so bound to be making mistakes haha!

Yep that was it :)  thanks!