"To get started, select the 'Remind me' button from the bottom of any note and choose the type of reminder you want to add. You can add time-based reminders for a specific date and time, or a more general time of day, like tomorrow morning. Adding a location reminder is incredibly easy too — as soon as you start typing Google Keep suggests places nearby," explains Google.
Here's the desktop Google Keep site:
The Android app has been updated and now supports reminders. There's a new navigation drawer with separate sections for archived notes and reminders and you can now add photos from the Gallery without using the "share" feature.
Google Keep integrates with Google Now, so all the Keep reminders are added to Google Now. You'll find them in Settings > My Stuff > Reminders. For some reason, the reminders added from Google Now aren't available in Google Keep.
You'll get notifications in Google Now, the Google Keep app for Android, the Google Keep app for Chrome (desktop notification) and the Google Keep desktop site (alert box), but you won't see redundant notifications. If you have both the Google Search app and Google Keep, you'll only get notifications from Google Keep.
When Google Tasks is discontinued (it will happen eventually), Google Keep will be the replacement. It's optimized for mobile and it doesn't integrate with Gmail or Google Calendar, but at least it's constantly improving and it has a cool mobile app.