We have improved the existing bookmark functionality in 2.5.0.beta3. All existing post_actions bookmarks will be migrated when you update your Discourse forum. Here is a summary of all the fancy new features 
Bookmark naming and reminders
When you bookmark a post or a topic a modal window will now show up with various options.
You can click save or simply click out of the modal and a normal bookmark will be saved, with no name or reminder (note how “No reminder needed” is selected by default). You can now also specify a name for the bookmark to help you remember why you bookmarked it. Otherwise you can choose from the following:
- Later today — Now + 3 hours, rounding to half-hour intervals. Cutoff time for this is 5pm (so 2pm is the latest you can select this option).
- Next business day — Mon-Fri at 8am. On Friday, Saturday, and Sunday this option will be Monday, the rest of the time it will be the same as Tomorrow.
- Tomorrow
- Next week — Now + 7 days at 8am.
- Next month — The current date next month at 8am.
- Custom date and time — Allows you to specify your own date and time for the reminder.
Any time the “Custom date and time” option is selected we we will remember the input you chose and next time you bookmark a post another reminder option will be shown:
- Last — The last entered custom date and time, as long as that date and time is in the future
Setting topic-level bookmarks and clearing bookmarks for a whole topic works the same way as what it used to.
Additionally, you can specify an auto-delete option for bookmarks:
Reminder notifications
We send reminder notifications in five minute batches, so delivery of custom reminders will not occur on the dot. This means if you set a custom reminder for 8:33am (if you are a very specific person) your reminder will come through at 8:35am at the earliest. Any failed notifications we will retry in the next batch. Bookmark reminder notifications are high priority which means they will be treated like PM notifications. They get a green notification bubble, and will stick to the top of your list of notifications until read.
Once a reminder is sent the reminder time and type is cleared but the bookmark remains. Clicking on the post bookmark icon opens the modal window to allow you to set a new reminder.
Here is what a bookmark reminder notification looks like:
Lists and navigation
The bookmarks in the quick navigation bar now come from the new table and will show you if you have a reminder set for the bookmark:
In the user profile activity page the Bookmarks link now shows a new list of bookmarks. From here you can see what you named the bookmark as well as the time the reminder will be sent. You can also search your bookmarks.:
Editing and Deleting
You can edit the name and reminder of a bookmark either by clicking the “Edit Bookmark” button from the actions dropdown in the bookmark list, or by clicking on the bookmark icon for a post:
Deleting a bookmark can either be done from the bookmark list or from the bookmark modal as a 2-step process (after you click on the bookmark post icon), and an additional confirmation is shown if you have a reminder set for the bookmark:
Keyboard Shortcuts
You can use keyboard shortcuts to select the type of reminder you want for your bookmark and to save the bookmark. A full list of shortcuts can be found in the ? help menu.
Syncing Reminders to Calendar
If you would like to see your reminders as events in your favourite calendar application, @Falco has created a .ics calendar feed. See Sync Bookmark Reminders with your favorite Calendar app for more details.
Still to come
We have a few future improvements planned including:
Improving the bookmark list
Recurring reminders
Reminder time parameter customisation
Any feedback on this new feature here on Meta would be appreciated 