Flash :

Google can now discover and index text content in SWF files of all kinds, including self-contained Flash websites and Flash gadgets such as buttons or menus. This includes all textual content visible to the user. Google supports common JavaScript techniques. In addition, we can now find and follow URLs embedded in Flash files.

Silverlight and other rich media formats:

Google can crawl and index the text content of Flash files, but we still have problems accessing the content of other rich media formats such as Silverlight. These rich media formats are inherently visual, which can cause some problems for Googlebot. Unlike some Internet spiders, Googlebot can read some rich media files and extract the text and links in them, but the structure and context are missing. Also, rich media designers often include content in the form of graphics, and because Google can’t detect words included in graphics, it can miss important keywords. In other words, even if we can crawl your content and it is in our index, it might be missing some text, content, or links.

read more detail here