There was a recent interview with a Yahoo! search top exec (name escapes me) saying they are no longer indexing the keywords. IIRC it was at a recent search event where all major engines had officials present.
One of my non-profit site has a 'competitor' that did some keyword spamming using my non-profit client's name. At that time ~43 pages were indexed and reported by me to the client in early 2008.
Older pages created from this spammy template do show up in searches using specific keywords. Newer pages created from the same spammy template in the recent past (2009-2010) still have the keyword spam in the header but DO NOT show up in Yahoo! searches.
Best guess at the timeline was mid 2009, but it could be late 2008 too.