You forgot Mother's Day. Again. With Father's Day coming up wouldn't it be nice to have a reminder among your often-used Google Now cards, in addition to the ones you've set in Google Calendar, Google Keep, and the sea of sticky notes attached to your monitor? It's possible to set holiday and movie reminders within Google Now on your device, but now you've got another alternative: setting reminders via a Knowledge Graph search on your desktop. Just make sure you're signed in, make a relevant search, and click that shiny new "remind me on Google Now" text.
At the moment there are a few limitations. Only well-known holidays and movie releases seem to be working - I tried to search for President Obama's birthday, for example, and did not get the reminder text. There's also no way to manually select how far in advance you'll be notified. Holidays will pop up into Now one week in advance, while movies will notify you on the day of release. Strangely, the only way to add a reminder from the Google Now app is to use a voice command -
mobile searches aren't showing the reminder icon. It wouldn't surprise us if more options are coming soon.
If you want to see a list of your current reminders or dismiss a few of them, open Google Now on your Android device and tap "My stuff" then "Reminders".
Update: As commenter lbrfabio points out, you can manually add reminders by searching for "add reminder" (and other strangely arbitrary commands) in Google Now.