This is a resurected post that has passed unnoticed when I posted it first due to low readership. Now there's more who can benefit from it.
X-Robots-Tag new HTTP Header that Google now understands and obeys has some further implications that pass unnoticed at first glance. At first sight it will allow indexing rules for non HTML files and so on but … was this a mini-hit on the link exchange industry? Learn to harness its power!