Clear Creative Commons licensing tools. Savvy uploaders can set Creative Commons licensing restrictions on any of their shots, both individually and in batches. By default, you can also choose what kind of licensing you want any of your shots to have, which makes it easy if you're a professional photographer to limit what people can do with them. In addition to giving you tools to tweak photo licensing, Flickr also provides fairly simple explanations of each license type, along with links to learn more. Also, photos that have been given more restrictive licensing can't be downloaded, making it easier to keep control of your intellectual property.
Easy uploading tools. Flickr's latest effort to make photos easier to upload to the Web is a big step up from their previous iteration. We took a look at the new version in August and came away impressed. Well, it's still worth using one of the software plug-ins to get right-click mousing access for contextual uploading on any photos from your desktop, the new Web uploader is really great for updating a ton of shots all at once while away from your home machine.
The API. Flickr's API has allowed for a ton of third party applications and services for both personal and communal use of photos. From business cards to coffee mugs, a hosted photo is more useful when you can do more with it than a quick glance.