Yahoo! recommends entering them to "improve the ranking of... results." (Despite this SEO pros still think meta keywords may be a waste of time.) I didn't find much open information on other search engines so I had to come up with some other way of determining their relevance.
I started by looking at the top ten search engines. According to SEOconsultants.com they are:
2. Yahoo! Search
3. MSN Live Search
4. AOL Search - Powered by Google
5. Ask - Powered by Teoma
SEOconsultants.com lists the remaining five in alphabetical order:
AltaVista - Powered by Yahoo!
Fast (AlltheWeb.com) - Powered by Yahoo!
Netscape Search - Powered by Google
Snap.com - Portions powered by: Gigablast, Smarter.com, SimplyHired.com, X1 Technologies, Inc. and Enhanced by Ask.com
The top four search engines (five sites, of which two run on Google) make up for 97.29% of the total volume of searches in the United States (for the 4 weeks ending October 25, 2008).
Coming in at #2 Yahoo! makes up 17.4% of all traffic. If they use meta keywords that could be reason enough to put them in.
Search engines do not publicize whether or not they use meta keywords. So in an attempt to determine if an engine thinks meta keywords are useful I've checked the source code for each of the search sites to see if they use meta keywords. My reasoning is that if a search engine uses meta keywords in their code it may be an indication that they think the "keywords" meta tag is important.
Here are the results of my research:
|Uses Meta Tag |
|Yahoo! Search|| |
|MSN Live Search|| |
|AOL Search - Powered by Google|| |
|Ask - Powered by Teoma|| |
|AltaVista - Powered by Yahoo!|| |
|Fast (AlltheWeb.com) - Powered by Yahoo!|| |
|Netscape Search - Powered by Google|| |
Some of these results are pretty interesting.
Yahoo! which recommends the use of the tag doesn't use it. On the other hand AltaVista which is powered/owned by Yahoo! does use the meta tag. I'm not sure why Yahoo! doesn't use the tag but AltaVista on the other hand has a history with "keywords".
According to SourceEngineWatch the "first major crawler-based search engines to use the meta keywords tag were Infoseek and AltaVista." Perhaps AltaVista is proud of once helping make the tag prominent? I can't say for sure. But whatever the reason the code is still in there.
(InfoSeek isn't in this top ten list of seach engines but they are relevant to this discussion. InfoSeek was bought by Disney in 1998. It was then converted into the search engine Go.com which still uses the keywords tag. ESPN.com and Disney.com, both Go.com subdomains, are consistent with their parent domain and use the keywords meta tag as well. I think it is reasonable to assume Go.com checks the keywords tag.)
The next oddity in this list is Netscape Search. Netscape Search runs on Google (who we know doesn't use the tag in their algorithm) so their use of the tag seems pointless. But it gets even more confusing. In 1998 AOL acquired Netscape. AOL also runs on Google and, as we can see in the table above, AOL does not use the keywords tag. Is Netscape simply holding on to an old tradition or does AOL not have a company-wide policy on meta tags? Unclear. But since they run on Google it doesn't matter.
From this chart I might guess that snap.com uses meta keywords but considering how inconsistent the other search engines are (Yahoo recommends them but doesn't use them, Netscape uses them but they don't make a difference on their engine) I wouldn't bet on it.
Yahoo says they help. Yahoo has a not insignificant amount of market share. I say go ahead and put them in. It might help your SEO at some non-Google search engines.