I'm on the side of those who think it's quite useless and very annoying.
To me, it's useless twice: once because it doesn't search in my phone and is not contextual, and is useless once again because most of the "extra features" don't work / suck / are not useful to me.
It's very annoying because is very easy to push accidentally.
I would like it to work much more with stuff on my telephone.
I want to listen to a certain song? Search button, swipe to music, I start typing and first it brings me to the song I have on my telephone, then eventually it can advertise I can buy it online...
It should do the same for places, for mails, for apps and for people. FIRST search in the apps, and THEN on internet.
As it is actually, none of the functions are actually working if the telephone has no internet connection.
In most countries, most of the extra features are useless even WITH internet. Just typed the name of the closest supermarket, nothing showed up under "places". Typed "U2", all I get is a web search, since Xbox Music is not available. Typed "shazam": no link whatsoever to download the app, just a web search.
Conclusion: is of the same use of a live tile linking to bing webpage, but occupies a lot of space that could be used in a better way and is darn easy to press accidentally.