I work from home with minimal external influences, so all of my contexts are available most of the time.
Once I start down a track, I tend to stay on it until something interrupts me, even if it's not the best use of my time. I have, therefore, added some context-based scheduling to force me to reassess what I'm doing every so often.
I'm finding I stay more focused on the task in hand when I know I've only got 25 minutes to do emails, before I move onto forums for 15 minutes, then writing projects for 30 minutes, then 10 minutes off the phonecalls list, etc.
It's all very flexible, and I can choose to ignore it if I decide my current project or context IS the best way to spend my time. But that little bit of structure is a good thing for me.