The Monarchy's profile hosts images new and old, ranging from a wedding photo featuring Queen Victoria and Prince Albert to more recent photos from the Queen's visits to New York City and Canada. There are even photos of the Queen as a baby. Each member of the family has his or her own set of photos, and there are a few more general sets such as "Latest News" and "Royal Events." The categories match those found at the family's website.
Buckingham Palace already maintains a Twitter profile, and it launched a YouTube account a couple of years ago. The Twitter account has a little bit more than 50,000 followers. It's not used conversationally, of course; it's merely a publishing platform for links to news stories and updates on the website.
The YouTube channel is a bit more interesting (though no more engaging) because it features interviews, speeches and documentary coverage of the activities and travels of the royal family. The videos are all promotional or informative in nature, and comments are disabled.
According to the AP, officials have said that bloggers are welcome to embed and share the photos from Flickr, however the images are watermarked "© Press Association" and no Creative Commons leeway is given. As is also the case with YouTube, you can't comment at the royals' Flickr account.