BuddyPress.org

Attach? As in upload? Never seen anything that could do that, yet, and don’t know why you’d want to, since activity disappears very quickly indeed off the page.

Embed, well, you can use the oembed plugin and/or the tinymce plugin (if you can get it working) or build your own toolbar above the textarea (search for ‘quicktags’ to find a thread I made for that (for forum posts, but it’d work fine for the activity update textarea too).