Last year, Macworld posted an update of an old trick from blogger Colin Devroe, which allows you to use your Mac to selectively remove photos from an iPhone or iPad without having to sync the device or download images. To do this, just launch Image Capture.
Image Capture sees your iPhone or iPad as a camera, just like iPhoto does. Unlike iPhoto, though, it doesn't make you import the images to your hard drive before you can delete them. To delete images off your iPhone, either select all of or do command-click to choose the ones you want to remove. Delete by hitting the red "no" button next to the import location on the bottom menu bar.
You can use Image Capture to upload iPhone photos to a different location. Say you've captured screenshots and want them in a certain folder on your external drive and not in iPhoto. You can do that using Image Capture.
Image Capture also provides in-depth data about your images, including date and time, location, aperture, focal length, shutter speed, ISO, location and if the flash was used. It's the sort of data you'll find when looking at the file in iPhoto, Aperture or another photo-management software, but it's still neat to see this at a glance.