How are the measurements used by Nielsen evolving to meet new methods of content delivery and viewing?

From Nielson.com (retrieved Dec 2012):

How We Do It

Panels

Electronic metering technology is at the heart of the Nielsen
ratings process. Our tools capture not only what channel is being
watched, but also who is watching and when, including “time-shifted”
viewing.

Nielsen’s TV families represent a cross-section of representative
homes throughout the U.S. Their viewing is measured by our TV meters
and Local People Meters which capture information on what’s being
viewed and when and, in the major U.S. markets, specifically who and
how many are watching. Additionally, we collect more than two million
paper diaries from across the country each year during “sweeps.”

Census

Using data from set top boxes, Nielsen delivers a constant,
real-time stream of information, revealing tuning behavior during
programs and commercials. We can tell clients which commercials are
being watched and which have the strongest engagement and impact. We
even analyze which position in the program or commercial block is most
effective for a specific brand.

Cross Platform Measurement

We measure national TV viewing using Nielsen's People meter technology
to electronically capture all viewing from our nationally projectable
sample of panelists.

Nielsen representative panels of Internet users provide browsing and
streaming metrics for online users. Using census-based measurement, we
provide in-depth tracking and analysis of site performance as well as
information about audience consumption of, and engagement with,
streaming media.

And for mobile media, we are pursuing on-device meter panels to record
every interaction users have with measurable mobile devices, which
complement our robust survey data.

Finally, through single-source panels along with modeled databases, we
measure how consumers engage with multiple media platforms.

There is a short video at the link above.