On May 6 2008, YouTube announced that “Starting today, signing up for YouTube means signing up for a Google Account that gives you access to YouTube, as well as other Google services such as iGoogle, Reader and Docs…So why are we doing this? We feel that by jointly connecting accounts, you can take greater advantage of our services both on YouTube and on Google, especially as we start to roll out new features in the future that will be powered by Google technology.”
But as search engine online guide ISEdb.com explains it [excerpt]:
One of the advantages for Google once users sign up with a Google account would be a significantly better targeting for its advertising both in and outside YouTube (Google Docs, AdSense advertising, Google News and Finance, etc.) thanks to the personal information gathered on the search giant’s servers. This is particularly important in light of the recent introduction of behavioral targeting for AdSense, which keeps track of the user’s interests to try and display to him or her messages that are most likely to attract his or her attention…Like many other popular search engines, Google collects search data for its users for the previous 9 months in order to achieve better targeting, with governments â€” particularly the EU court â€” pushing for such a limit to be reduced to 6 months or less. However, there is no restriction for the gathering of non-search related data including YouTube and Gmail among others.