A great feature of iPhoto is it's ability to subscribe to RSS feeds with images in Apple calls these photocasts.  This means you can continuously view friends and families photos as they are updated.  The only problem with Photocasts is that you need a costly .mac account to create a stream of you own.

Flickr has a similar feature for producing an rss feed full of images, and it turns out that it's compatible with iPhoto.  There's only one hitch - the images are too small to use in a full screen slideshow especially if you have a big screen.

I took a look at the RSS feed and found it all that was required to make the images large was to alter a few letters on the URL of each image.  I was considering writing a program to do it but then I rummaged around the web for a while and found the marvelous Photocastr - a site which automatically converts Flickr feeds into Photocasts with good quality full size images!