Reading through the Flickr API documentation it keeps stating I require an API key to use their REST protocols. I am only building a photo viewer, gathering information available from Flickr's public photo feed (For instance, I am not planning on writing an upload script, where a API key would be required). Is there any added functionality I can get from getting a Key?
Update I answered the question below
The Flickr API is very nice and easy to use and will be much easier than scraping the feed yourself.
Getting a key takes about 2 minutes - you fill in a form on the website and then email it to you.
Well, they say you need a key - you need a key, then :-) Exposing an API means you can pull data off the site way easier, it is understandable they want this under control. It is pretty much the same as with other API enabled sites.
To use the Flickr API you need to have an application key. We use this to track API usage.
Currently, commercial use of the API is allowed only with prior permission. Requests for API keys intended for commercial use are reviewed by staff. If your project is personal, artistic, free or otherwise non-commercial please don't request a commercial key. If your project is commercial, please provide sufficient detail to help us decide. Thanks!
If you have a key, they can monitor your usage and make sure that everything is copacetic -- you are below request limit, etc. They can separate their stats on regular vs API usage. If they are having response time issues, they can make response a bit slower to API users in order to keep the main website responding quickly, etc.
Those are the benefits to them.
The benefits to you? If you just write a scraper, and it does something they don't like like hitting them too often, they'll block you unceremoniously for breaking their ToS.
If you only want to hit the thing a couple of times, you can get away without the Key. If you are writing a service that will hit their feed thousands of times, you want to give them the courtesy of following their rules.
Plus like Dave Webb said, the API is nicer. But that's in the eye of the beholder.
We set up an account and got an API key. The answer to the question is, yes there is advanced functionality with an API key when creating something like a simple photo viewer. The flickr.photos.search command has many more features for reciving an rss feed of images than the Public photo feed, such as only retrieving new photos since the last feed request (via the min_upload_date attribute) or searching for "safe photos" only.