Some of my widget options have mysteriously disappeared, for example the 'Image' widget. This is for my multi-site installation, that includes some sites like CanadaCloud.net.
I experienced this problem before, and it seemed to be that my sites had been disconnected from Wordpress.com, and these were Jetpack ones. So they disappeared. When I re-connected the sites they reappeared ok.
However the sites still seem to be connected but the widgets have disappeared again, this time I don't know why.