This is just another step before google takes over the world, mark my words. :P
I'm not necessarily against Google owning a lot of the technology/online market. They do a good job of up-keeping most of their stuff.
If it was any other company, sites would be down all the time.
True, having everything linked to one account means if that account gets hacked you're gonna be screwed, but Google has some pretty good security (YouTube accounts got hacked all the time before Google bought them out, now its very rare and usually the victim's fault for giving out info)