With the release of public beta of Windows Live Hotmail Wave 4, the service's more than 360 million active users can enjoy several key features powered by Silverlight, mostly around sharing documents and photos.
"Silverlight allows an efficient upload of multiple attachments, by giving users option to send them as links to online files. The files are then uploaded to Live SkyDrive, where users get 25GB of free online storage space. Furthermore, having Silverlight installed provides best experience with viewing attachments: new "Hotmail Active View" uses Silverlight to allow attached photos to display in a slideshow.
Also, Office documents, such as PowerPoint presentations, are sent to Hotmail can be opened via Microsoft's new browser-based Office Web Apps that use Silverlight to optimize viewing experience. With Silverlight, Hotmail users will therefore be able to view and edit an Office document in their browser, even if they don't have Microsoft Office installed on their PC."