how important is meta description in page ranking. how many key words are reasonable in meta description.
Meta description has little to no importance in rankings, it should normally consist of 30 keywords length or 260 characters max. Might be less or a little more, does not matter much.
Add a few magical "meta tags" to your web pages, and you'll skyrocket to the top of the listings. But Wait! If only it were so easy. Let's make it clear: Meta tags are not a magic solution. Meta tags have never been a guaranteed way to gain a top ranking on crawler-based search engines. Today, the most valuable feature they offer the web site owner is the ability to control to some degree how their web pages are described by some search engines. They also offer the ability to prevent pages from being indexed at all. This page explores these and other meta tag-related features in more depth. Ideal character/ words limit in title = 60 - 80, meta-description = 150. But it may change with time span and SE.
IMO Meta description is not important in page ranking however Meta description is still important for SEO. They are show as description when searcher search through search engine. So alway write the description that searcher want to click. Yes, sometime Google use page content as description but still there are 50 characters or more from meta description included. So it is still important for SEO.
Meta descriptions are very important when it comes to proper on-page optimization, not only do they play a role when it comes to understand the content of your web page they also provide searchers with a quick description of your web page in the search results. Make sure to use an accurate human meta description, don't try to just stuff in keywords.
And if you really want to see your click-through rates soar through the roof, learn how to write them with a compelling call to action as well that compliments the page title (the contents of the <title></title> tags).
Its not much of importance for Google; but some other search engines do care much about that. So its better probably having it. Even with Google I like to have it just because I don't think bots always would find the right piece of description from the page. Just my thoughts