I'm been using the Google Maps API for a few years now on various projects. Developer nirvana is often being able to integrate different APIs to get an entire entirely different project. Like for example merging Flickr geo-located photos onto a Google Map.
Recently my company released a website allowing registered users to upload photos and videos using their online control panal to store files on Flickr and YouTube. We used the excellent Flickr.NET wrapper and Google's own .NET class library for the YouTube integration. Approval of images and videos were done using a custom CMS tool on the website allowing content editors to preview the multimedia uploads before making them visible, using calls to the respective APIs to change permissions. It worked pretty well, although uploading large video files is definitely something your average user still struggles with. You can see the end result here.
While trawling the internet trying to figure out how to implement the various API integrations I came across a website at mapaset.4bcj.com that allows you to create your own Flickr/Google Maps mashup without doing any coding at all. Its basically a clever mashup wizard. I think its part of Brett Jones blog, but there's very little information about it.
The UI could maybe do with a bit of work, but its a great idea. I really like how the application can use different ways to access your photos, such as username, email address or even the URL to your photostream. Very clever and generated results are pretty good. Here's an example of it using the code generated on the site to show a bunch of photos from recent trip to Laos.