Local Silverlight guru, Liquidboy (Jose) has put together a sweet ball of code which essentially allows you to upload Flickr photos in Silverlight (via OpenFileDialog Class).
I won't echo what he's done (as he does a far better job than I ever could), suffice to say check it out as it's worth the read.
http://advertboy.wordpress.com/2007/12/20/flickr-multi-picture-uploader-done-in-silverlight/
I cannot get enough of his efforts!