The NielsenWire headline screams, "Total Online Video Streams up 41% from Last Year." So video viewership has gone up significantly, right? No, not as much as 41 percent would suggest.
Streams per viewer in August 2009 were up about 20 percent over August 2008. Now, 20 percent is still a lot, but it's not 41, especially because the total number of unique viewers "only" went up 18 percent.
So – there are more people watching videos, and each person is watching more videos (instead of working, sleeping, etc.).
These metrics are especially relevant if you've increased your commitment to video over the past year. Has your investment paid off as much as it should have? Are more people watching your videos? Is each visitor, on average, viewing more of your videos?
I'd also toss in metrics – like the percent of viewers who started watching videos but didn't finish them – that indicate whether your content is working.
There are technical and vendor reasons to know the total number of video streams, but this metric is not very useful for news decisions.