When people try to perform two or more related tasks either at the same time or alternating rapidly between them, errors go way up, and it takes far longer--often double the time or more--to get the jobs done than if they were done sequentially.I know I've been making more effort to stop multi-tasking. One key for me to get something done is to shut off distractions; don't look at email, close out of IM, close the browser, so I can focus on the task at hand.
The article goes on to say a little stimulation can help but to much gets distracting. I like listening to traditional Jazz (no lyrics) when I'm trying to focus. Nothing like some good Coltrane to help get that spreadsheet done.
Another interesting fact, the mind needs quiet time in order to help memories form. Another reason for meditating. On the same line, it's important to get away from all the technology and have some interactions with people.