Here's the problem as I see it: Like many knowledge workers, the vast majority of my daily tasks are now entirely computer based, and most of them require an Internet connection. I spend my day doing online research, reading and sending e-mail, writing a lot of stuff, occasionally filling out expense reports or otherwise dealing with bureaucratic shenanigans, and making the occasional phone call. Almost all these things can be done wherever I have a and a --which is pretty much everywhere I ever go.
Essentially, two forces--the convergence of my daily tasks onto cloud-based resources and the increasing ubiquity of access to those resources--are making my present location in physical space practically trivial. These days, only a very minute number of my tasks require me to be in a specific location, and most of these revolve around my responsibilities as a parent and a husband, rather than as a worker. So why should I bother tagging any of my tasks with '@computer' anymore?
The answer, at least for me, is that there's almost no point whatsoever in differentiating task contexts on the basis of proximity to phones or computers anymore. Earlier today I conducted an interview with a remote contact while browsing background resources on my 3G and taking notes on paper (yes, I still use that stuff), all while sitting in a Berkeley pub and sneaking the occasional nacho. More and more these days, the tools of my trade can be almost anything with an Internet connection, and because my important stuff all lives in the cloud, it doesn't matter much whether I even use the same set of tools from day to day.
Just because location-based contexts have lost relevance, however, that doesn't mean I don't use context tags anymore. Instead, I just define contexts more dynamically. Now, instead of '@computer' or '@phone', I'm much more likely to use people's names as contexts.
When I'm jotting down a task that needs to be done the next time I'm with my wife, such as discussing options for our next vacation or exploring college savings plans, I can tag these '@christine'. That way, when I get home I can just pull up all the tasks with her name as the tag and run through the checklist. This basic approach works as well for colleagues as it does for family members, of course.
Of course, location tags still have relevance, but in a broader sense now. I'm still apt to use '@hardwarestore' or '@mall' for shopping items. And I still like to keep lists for things to do on my next visit to a particular town, as in '@austin'.
My favorite tag of all, however, is '@braindead," which I use to tag to-do items that aren't particularly time sensitive but can be accomplished with almost no psychic energy.
So despite the fact that I'm now almost constantly in front of some kind of computer or phone, and I nearly always have an Internet connection, tags have retained real significance in my productivity system. If you've abandoned tags in your own system, you might consider reintroducing them in a more flexible way.