I like the idea, personally. I don't see much downside to extra embedded information. I imagine it will sort of be like the built in Kindle dictionary, for the people who use it, it's an amazing and much needed feature. For those who don't use it, I'm sure they don't even give it a second thought as they read.
I think we live in an age of options, but it's always a good idea to be able to turn those options off. Which it seems Vook understands well.
It reminds me a bit of the "Annotations" on YouTube videos. Sometimes I find some much needed information in those, and sometimes -- when I simply want to watch the video -- I turn them off because they annoy me.
I just like being able to decide when I want it.