Here's what I do...
I'm the controller for four very different companies - a heating oil company, an internet start up, a restaurant, and a real estate trust. As you can imagine, it's hard to bounce in and out of the different companies all day, every day.
I have one email inbox, one main paper inbox, and four smaller paper inboxes, one for each company. I print out every email that requires some thought and "file" it in the appropriate inbox. (The big inbox is for stuff others give to me. That gets processed into the four inboxes when I get a chance.) Once the emails are printed, the digital copy gets dumped in that company's folder. That's all the email sorting I do - when I'm ready to reply to that specific email, I search for it. If it's REALLY important, or it's someone I don't email often, I leave it in my inbox so I can find it easily. I know - that's against the rules, but it's easier for me.
I work in terms of companies, so I guess you could call that my context. (I've also tried categorizing them as projects. I don't have an answer as to which is best.) What matters to me is that when I'm in "Heating Oil" mode, I know what my next actions are. Most of my tasks are the same ones every day, so I don't really have lists of next actions or true contexts. When I do need a task list, I use OmniFocus on the iPad. I live in the forecast screen and ignore the rest of it.
I tend to spend my mornings on the "easier" companies and my afternoon in the heating oil world. I don't always get through all the companies on a daily basis, but I rotate the smaller ones and I always have a note somewhere to remind me if I HAVE to do something company specific by a certain time. (Outlook calendar, OmniFocus, index card, email from micromanaging co-worker )
All my handwritten notes, file folders and binders are color coded to a specific company, so if I should misfile some notes I've written - which happens too often! - I know within seconds where it is. (Blue paper sticks out in a yellow file folder.) Unfortunately, to keep life a little simple, everything gets printed on white paper. If I had a printer with multiple paper trays, I'd be printing on the appropriate colored paper!
The nice thing I've found about GTD is that you don't have to "do" GTD to reap the benefits of having its structured system.
"My feeling is that labels are for canned food. I am what I am, and I know what I am." - Michael Stipe