In Google Terrorists on Yahoo, Philipp Lenssen asks
When you search Yahoo UK/ Ireland for "google", the fifth result will be for... "www.google.ca/#terrorists". What's that, a Yahoobomb?
[Thanks Eric of Mechanical Turk Monitor.]
Update: Something similar happens when you search Yahoo.com for "mcdonaldsforshizzo" (the second result for me is "www.google.com/#mcdonaldsforshizzo"). [Thanks Maurizio M.]
(also Search Engine Watch)
These seem to be results of web-spamming, perpetuating itself by pages being scraped and re-scraped. It's not clear how it started. But I conjecture the tag after the "#" seems to be so that they can track which spamming pages are working.
Yahoo is being affected by the spam-pages.
Here's some examples (*not* linked, since these are spam!)
http://www.google.com/search?q=cache:7J67NvwZsgYJ:community.jyve.com/index.php
http://www.google.com/search?q=cache:oBjjhB7C9mMJ:www.selectedlink.com/worldweb/canada%2Bsite.html
http://www.google.com/search?q=cache:TDBiUu8a46AJ:198.65.112.65/search/results.php
http://www.jolt12.co.uk/google_search_engine.html
(note there's a tag "#darwin" there)