I’ve been using Media Tags plugin with much success – it was very useful for retrieving images belonging to certain page with specific tags with following code:
$results = get_attachments_by_media_tags(array("media_tags"=>"gallery", "post_parent" => $global_id, "order" => "ASC"));
Of course you can easily tag anything that sits in your media library (I wasn’t even aware that you could tag something during upload time). As for tagging during upload with browser uploader – it might be too much too ask 😉