On the dev branch this week we have a good collection of issue fixes and feature requests. The dev branch commit log has all the details. One feature added this week which I think could come in very handy is #520 (via @Jonathan Lahijani) which adds the ability to hide individual images in an images field. When an image is hidden, you can see and work with it in the admin, but it gets removed from the field value on the front-end of the site at runtime, effectively hiding it. I know I'll use this a lot, particularly on photo galleries where I may want to remove an image or two from appearing in the grid of photos, but don't necessarily want to delete them.
Images can be hidden (or unhidden) from the Actions select of each image, where you'll see a "Hide" option (or an "Unhide" option if the image is already hidden). Hidden images are also dimmed out when viewing the images field in the admin.
On the API side, you can hide or unhide images and files using $image->hidden(true) to hide, $image->hidden(false) to unhide, and $image->hidden() to get a true or false as to whether or not the image is hidden. Though this will only be useful on unformatted field values, since hidden images are automatically removed from formatted field values.
The same can be used with regular file fields, but we don't currently have a UI/interface for hiding or unhiding items from regular (non-image) file fields. Likely we'll add one soon, but I figured it's likely to get more use with image fields than file fields, so figured we'd start there. More next week. Thanks for reading and have a great weekend!