meh, this will become more of an issue as more and more apps and template based technology becomes more and more common.
For online players, I can definitely see the appeal because playing live must be like watching snails race for them...
I do think they will miss out on some valuable info by not paying attention to the live game they are in. Multi-tasking is one of the biggest myths perpectuated in the 21st century.
Lets say you can do one task with 90% efficiency. Well, if you split your attention to two tasks, then you end up doing each of the two tasks at like 60% efficiency. Split your attention into 3 tasks and you end up doing each task at like 20% efficiency...
And this definitely gets worst if you use the same portion of your brain for each task.
But hey, if you feel that your 60% is good enough, then by all means, play both simultaneously. Eventually your results will push you one way or the other.
We had a guy who liked to play online and 2/5NL at the same time. He lost $5K in a couple of sessions and stopped doing that pretty damn quick