Use machine learning and neural nets to use tag generative tag clouds based quick scrape of the headers, title, content of the website and use user feedback to classify the data and train the AI. You can then use this same neural to be trained for collections and nested collections, etc. I think this feature is very useful because bookmarking is easy but organizing bookmarks is like looking for needles in haystacks. So much tedious tagging and collecting can be automated with user feedback to classify AI predictions with confidence.

Warn users when adding a duplicate bookmark. This would show them where that link already exists, saving time from duplicate cleanup later on.

Its great update. I've been using raindrop.io since the first launch !!!

Maybe another right click option like 'Save screenshot to Raindrop.io ' with options to save the full page, the visible area or the one I would use the most - save selection where you can select the area on the page you'd like to save. The new built-in Firefox 'Take a screenshot' has great functionality for reference. This feature would be really helpful for bookmarking favourite UI component designs and I imagine would be a big draw for designers out there

I believe it would be fantastic to add the ability to set descriptions for collections themselves. The description could be positioned directly underneath the collection search bar when a collection is selected. This would allow the more ambigous collection names to describe themselves, rendering it especially useful if the collection is shared with others.

parent & children tags to form a more useful taxonomy

In this time, I am on the horns of a dilemma cause I want to add my bookmarks into multiple collections without duplicate them. I'd like that feature as soon as possible =)

Blank page for note-taking or pasting written content. This would elevate and beat other note-taking software.

Like "Smart playlists" in iTunes. You create conditions (topic, title/description/text contains string, multiple tags, type, date..etc...) and all bookmarks automatically puts to specified collection. Think of it as "saved search"