Mike McLaughlin at VersionOne:
Sometimes you’re being asked to be a member of several project teams at once. Other times, you’re being yanked off an active project (with little to no notice) to work on a pet project for a C-level executive. Telling your boss the consequences of such actions is hard to do, but necessary. And if they’re a good boss, they’ll actively listen to you, empathize, and try to remove any impediments that stand in the way of you getting work done productively and of the highest quality.
Context-switching is one of those things that creeps up on you. Each acceptance of a new, parallel task adding to the penalty. Sometimes there is no alternative; we must acquiesce to additional deadlines. But in these instances, we owe it our teams and the requestor to help them understand the negative impact.