The amount of time viewers spent watching TV while at the same time cruising the Internet grew 34.5% last year to an average of 3.5 hours a month in 2009, up from 2.5 hours in 2008, according to a Nielsen Co. report released this week.

Nielsen says nearly 60% of TV viewers now use the Internet once a month while also watching TV — up 3% from a year before. The survey also notes that the number of people who are multitasking grew almost 5% from the year before to 134 million.

“The report seems to suggest that concerns by TV executives that the Internet was taking people away from their shows are unfounded. In fact, live TV viewing increased 1% in 2009. Add in time-shifted viewing a la TiVo, and the average number of hours jumped to a total of 163 hours a month watching TV in 2009, up from 160 hours in 2008.”

So what are people doing as they watch TV? A look the top 5 sites visited by these media multitaskers gives some clues:

Google
Yahoo
Facebook
MSN or Microsoft Bing
YouTube

But is multitasking really a good idea? … Sorry… just got a text… Right, CNN.com says heavy multitaskers are more easily distracted by irrelevant information than those who aren’t constantly in a multimedia frenzy, according to a study in the Proceedings of the National Academy of Sciences.

Even when you think you’re doing several things at once, you’re more likely switching rapidly back and forth between them — actually compromising productivity. Plus, multitasking puts stress on your brain’s memory-retention center…

Wait, what was I doing?