One of the biggest hurdles in getting things done is figuring out how YOU will get things done. Don't force yourself into the classic contexts. I had an @Email and @phone, but ultimately I decided that the big picture is that I have to contact someone. So now my context is (of course) @contact. Similarly, there are things I need to look up online (@Web), but I also I may need defrag my hard drive or install a new software package (@computer). Now I just have @PC.

You see that by worrying about knowing what specific context you need to put a list in, you have created mental anxiety and haven't moved forward, the whole point GTD tries to address. But the truth of the matter is that everyone goes through it. The key to being successful is reviewing your lists. Reviewing is what helps you remember what you need to get done.

To your point that there are things which you can do at home OR work, my resolution to this is simply put the task in the context that I'll most likely complete it. But again, I find that when I review my lists regularly, you keep a mental note of those things which can be done in multiple contexts. That way when the time arises, it will trigger in your mind that you have the opportunity of completing that task.

The more and more I try to get my GTD system down, you think there should be a support group or something!

I have a few contexts (@work, @home, @pc, @phone, @errand) which are all locations (could be tags if you prefer).

Then I have a few smart lists that combine these locations. Example:
I have a smart list Work which among other things filter these locations: (location:@work OR location:@pc OR location:@phone)
I have a similar one for Home.

Hope that helps.

Contexts are whatever you need them to be. My business is originating commercial mortgages so my contexts follow my needs @Calls, @Leads, @Underwrite, @LoanSpecific#. I also make extensive use of tags.

The beauty of it is that the contexts are what work for you. They do not need to be exactly what works for someone else. Context descriptions are tools not the holy word from on high.

Why not use multiples tags for your contexts. For example I have to write an email today. I just add @computer to that task. So when I make a smartlist for only @computer it will show me all the items I should be doing while at a computer.

In the same way if I want to see all the things I need to do at work today I use the smarlist that Rajjan suggested above. Now the great thing about tags is that just because its tagged as @work doesn't mean I can't tag @home also.

So if I want to "read a journal article" I can tag it both @home and @work. Now when I use the smartlist to filter @work, I still see the task is visible. Then when I get home and I look through my list it shows up there too as long as I haven't completed already.

I think the secret to GTD is not only getting all the things out of your head, but also limiting the tasks that you are confronted with so that you don't become overwhelmed.

I've found it works much better for me to have a single list for each context, and use tags to represent projects. Then I can use the cloud on the sidebar to hone in on a specific project, or just look at a particular list when I'm in a certain context.

In response to the original poster... I definitely use multiple tags for a lot of things, because context is not as cut and dry as some people make it out to be.

I find the @phone context useful because when I get to doing phone calls, I like to get a bunch out of the way at once. And it would be nice to see that tag go away from my tag cloud once there's no pending calls I have to make!! If I have to do a phone call at home for any particular reason, I will mark a task both @phone and @home.

I think that an @online tag might be useful for people who find themselves distracted by the internet when they really should be doing something that doesn't need it. Then if an idea comes to mind of something you want to look up, just task it, tag it, and don't look at it again until later. Unfortunately, I am constantly looking stuff up for my research work, so I really can't do this.

I do have an @pc tag, which I sometimes use on its own, and sometimes use in conjunction with an @home tag, if the task should only be done at home (such as home pc maintenance or online banking). Once I get a laptop I'll probably have a tag for that... hmm, or maybe that would be a project....

The big thing for me is that I also use tags for projects, prefaced with a different symbol depending on whether it's for +work or -home or .play. And I'm using the tag organization idea from the thread linked in the original post -- love it. But because I use so many tags, I'm very glad that the new feature of seeing the tags in the task list can be turned off. Kudos to the RTM team!

My Smart Lists look at tags, and so when I'm in "@work" mode (not an actual context tag nor location) I can browse all the tasks with work-related tags or that involve me being on campus (I go to the campus doctor, so that's not work-related but I need to see the info in my work list or else I'll forget).

I'm still just starting out, and getting used to relying on my system... and I too have been struggling with context. Merlin Mann suggested that some of us need to be reminded to get ourselves away from the pc, and I've been thinking I need to do a NOT(tag:@pc) search a little more often. :)