I needed to find a particular post. After failing to find it with search, I recalled that it had an attachment. It would be nice if there was a checkbox on the advanced search page for "has attachment(s)" to only return posts with attachments. Thinking about implementation, I think it could be kept pretty simple. If you check the box, the posts have to have at least one attachment. If you don't check the box, it doesn't matter if the post has any attachments or not. Of course, you could go further and allow searching for posts the do not have any attachments, or even search for number of attachments, file type, file name, etc, but I think all of that would be unnecessary. Just one simple checkbox-- "Search posts with attachment(s) only".