For example, I have nicheforum.com (not my actual site, this is example). In my meta keywords tag should I put: niche,niche forum or : niche,forum Does google or yahoo penalize for duplicate keywords ? Also at some seo website I read that major search engines began to completely ignore meta keywords section. Is that true ?
These days meta keywords are ignored by Google (mostly 99%+) but yahoo and google can be a good candidate so must put meta keywords and description (most importantly). Imo niche,niche forum could be more worthwhile (though worth is very low).
Personally, if you're going to use the meta for keywords I either simply use niche forum or niche forum, niche to separate the "niche" to be safe.
Click below and put your keywords in to see how many times they have been used lately. Have a look at variations to see what will work for you. http://66.35.238.14/d/searchinventory/suggestion/
Based on your example, I'd go with 'niche, niche forum' - these will be viewed as separate keywords by the SEs. Listing only 'forum' as a keyword is too general, and does not accurately represent the content of your site. Sam