I've held off for a while with this topic...wow...page 7. I think context is important!
I love context. I tag every Next Action and Project with as many tags as appropriate. They help me a lot!
If a NA has a person associated with it I tag it to that person. Then when I am with that person I select their name and EVERYTHING I have with them comes up. This saves me all the time. I also tag with locations...I manage a facility with 25 buildings divided amongst two campuses. Tagging by location saves me all the time too.
I really feel Contexts is one of the best things about GTD.
iPad, iPhone, MacBook, PC; all running Nirvana, iCalendar and GMail
Mastering Workflow (2012 & 2013)