I used to take 30mg xr everyday. I could train for hours, but I could hardly eat until late night when it wore off. I stopped taking it for a couple months and gained 15 solid lbs. Yes, solid, barely any fat. I stopped taking it to join the Marines, and I do not regret doing so. I find it harder to get motivated, but I just crack open a red bull or drink some coffee for a nice jump. Also, it is much easier to sleep without it. Also, my grades slipped when I went off the medication, but in the end of the day, I feel good, so it is all good with me.
My advice to anyone taking the time release, switch to tabs and break them into pieces. that way, you can take only a bit at a time and only take it when needed. you will find that popping 5-7mg once a day will wake you up in the morning and for teh rest of the day you should feel pretty good. time release is garbage in my opinion, and i would know, having spent a couple years on it.