Niall Ginsbourg (a Media Center community development expert and the developer behind the Big Screen Blog) is working on an updated version of his Big Screen Photos Flickr photo viewer for Windows Vista Media Center.
You can check out the blog post at http://mobilewares.spaces.live.com/Blog/cns!78533A1A2E078194!395.entry. It contains example screenshots and a video of the work-in-progress new version of Big Screen Photos. As the post indicates, the new version will support all of the features of the original version, and has some visual design changes to make it look and feel more like the Windows Vista Media Center UI.
The screenshots and videos look good, and I encourage you to check them out if you get a chance. After looking at them myself, I'm looking forward to trying out a beta version of the application.
The original version of Big Screen Photos is a Windows Presentation Foundation (WPF) XBAP application that is integrated into Windows Media Center and can also function as a standalone application. The new version is being implemented in Media Center Markup Language (MCML) and the Windows Media Center Presentation Layer (WMCPL). As Niall gets farther along, I really hope he'll volunteer to write a comparison study between implementing the Big Screen Photos application in WPF versus implementing it in MCML/WMCPL to help other Media Center developers make a more informed decision about what technology to choose for their applications (hint hint Niall....)