From working with coffee and espresso 40 hrs a week or more, yes you will build an immunity to the caffeine. I can take to shots of espresso, go lay down and fall asleep like that. The stuff is like water to me. the drink that gets me going a little bit now:
A Venti Starbucks Double Shot with 8 pumps White Mocha, 6 pumps Pumpkin Spice, Breve and 2 Added Shots (total shots = 8)......thats my morning drink right now =)
once that doesnt work I will go up a shot lol