I am a graduate student (about to return to undergraduate but that's a different story) and I have two student worker jobs on campus, all of which gives me a lot of discretionary time and that is really dangerous for me. My work duties and both jobs never take more than an hour to complete and the rest of the time is basically just being there to answer the phone, answer questions, etc. I also spend a lot of time at my local Einstein's Bagels shop in the mornings. Ostensibly, all of this discretionary "free" time would help me GTD, but I find that I have a huge difficulty naming my context. For instance, @Work could mean reading that reading assignment for class, doing my Greek translation, writing code, pissing away time online, research on the library's site, writing some on my four term papers that aren't due until the end of April, learning Croatian, posting on board.43folders.com. I think you get the idea. So, when I sit down at work or Einstein's, I have so many options of what to do that I usually go with pissing away time online since my school's wireless internet reaches to Einstein's. Even without the internet, I can find a way to piss away two hours in a hurry.

So, how do you identify what it is exactly that you should be doing in ambiguous contexts? Or am I making this into something it's not when I should just be more conscious of the issues I mentioned above?