How can Google expect users to trust them with an app when they could shut it down at any time. No thanks Google.
I have more faith Google keeping Google Keep alive than Reader. From the data mining perspective it makes a lot of sense:
Reader gave them data on what you read, what sites you're interested in, but even this was a—potentially huge—haystack from which Google still had to pick the things you're really interested in, only slightly aided by the fact that you might've shared one or the other article using the buttons on Google Reader's web interface.
Google Keep will give them insight into the things that are important enough for you to have them saved permanently. It has the potential to give them data that's more useful than what they get from search, because you're doing the filtering and the only thing you save are the pertinent bits. It removes a huge amount of uncertainty for them.
Combined with data gathered through their search products and various social networks, Google not only knows what it is you're really interested in, but—in some cases—also how you came to acquire that information. After a while this'll make predicting your (re-)search behaviour and decision process a lot easier for them.
Last but not least there's the data from the real world that you input that Google might've had close to no access before. Users will be saving photographs of information they need to remember in there, maybe some documents and other random pieces of data that Google would've not seen before. All available for them to analyse and store.
What this means for Google is the ability to tell their customers that they have a more complete picture of the product (= you) they're buying.
As an aside:
I've been an Evernote user for many years, since the first private beta actually, and even though the service has many problems and I've pretty much stopped using it, I was glad that it has always been a service that didn't rely on the company selling my data to make money.