I think multi-tasking is best-suited for jobs which don't take too much brainpower. I right now am listening to Fox for news on Operation Mountain Lion, posting here, running a load of laundry, and doing spot cleaning during the commercials. None of this requires my undivided attention.
If I were trying to write an article with links, or doing taxes, I wouldn't have the TV on and would be focussing only on the task at hand.