Can't seem to pull yourself away from Facebook/Twitter/email accounts?? (Although I am quite sure our lovely new UMBC/Google account isn't too much of a problem to stay the hell away from)- Mac's got the Narcan for you fiends in the app "SelfControl". You set your blacklist of sites and email servers you know you need to refrain from during study/class time, set the amount of time before you can guiltlessly indulge, and you are officially ready to be focused like never before.
Be advised you won't be able to re-boot your computer or the internet or erase the app to re-set it. The time you choose will have to run out until you are once again allowed to log on to whatever brain surping site of choice. Sounds a little daunting but, if you can have enough self control to install it I'm almost certain your GPA will thank you for it.
Happy studying!