I use Siri all the time to remind me to do things. Pay a bill tomorrow morning. Buy milk the next time I'm at the grocery store. Brush my dog. Thanks to this OS X Daily post, Siri has become more useful because I now use her to remind me about long-form articles I don't have time to finish, emails I need to respond to later, and new recipes I want to try.
When you are viewing something that you want to be reminded to return to later, call up Siri by pressing and holding on the Home button or by saying, "Hey, Siri" if you have that feature enabled. With Siri listening, tell her to "Remind me about this" and then give a time or location.
I used Siri today, for instance, to remind me about a New York Times article tomorrow morning when I'll have time to read it, about a Bolognese recipe the next time I'm at the grocery store, and an email from Netflix about a newly added movie that I might want to watch tonight.
The reminders are added to your default list in the Reminders app and each shows the app icon of the app you were using when you created the reminder. You can wait for the reminder to arrive as scheduled, or you can go to the Reminder app and tap the app icon to open up the page you were viewing when you created the reminder.
In related news, you can use Siri to check business hours.