Emotional Multitasking

This morning, I was chatting on IM, checking email, and reading an article for class (a typical Friday morning). As I was doing this, I found myself wondering about how people multitask at an emotional level. Since working memory is limited to just a couple items (7 +- 2) at a time, people who are good at multitasking are those who are good at quickly swapping task-related data in and out of memory. What sort of effect does this have on emotion? For example, if you were IMing with someone about happy news, but reading a very sad email, would your emotions fluctuate as you flipped between the two items? Would the stronger emotion dominate, or would the other emotion help to temper it?

Also, there must be some sort of cost for trying to mediate the different emotions associated with each task. With so many concurrent forms of emotional stimuation, its no wonder stess levels keep going up.