Title: Distinct on EACH page of you site meta tags: Short list of the keywords you are targeting description: Distinct on Each page of your site I really can't say what direct effect these have on SERP's, but I can say that having distinct information per a page will help each page get indexed and not be a supplimental result. Others may have more info for you...
ime its useful to add meta description tag. I don't think it helps in seo. But i believe it increases CTR when your page is displayed in serp.
Google still shows your site's title and description tags. I don't think it helps much in seo but it looks better if you have a good title and description.
SERP's and CRT are not directly related... Why leave anything to chance, put them in it will only take a few minutes...
Meta tags are still important, as it has already been said I don't know what effect it has on your SERP but it's important as to what is displayed about your website on Search Engines, I tried for a month not to include meta tags and meta keywords in my blog, haha it was funny to see what was displayed, the Search Engine just took a random text from the blog to display as description.
meta tags aren't l important for your SERPs!!! rember that ! but also remeber that you never known how the next google algo will be so maiby tomorow it will be the most important thing on the earth for google eyes I did a test and posted it here something to covince via examples that some tags aren't important at all ! The link for META TAGS expirement is here: http://forums.digitalpoint.com/showthread.php?t=97008
Meta tags are useful. Infact Meta Description tag is too important for getting good rank. Also SEs use it as a description in Search Engine Listing. Only Meta keywords importance is sligtly reduced. But it is good to list your important keywords in Meta Keyword tag. You should try all things as far as it won't hurts you ranking.
I would recommend to add META keywords, and description tags. Beside that you should have a unique title for everypage in your website. META description should be short and informative.
even i do recommend all to have META keywords, title and description as there are few other SE's too that extract data from the META's... although they are not considered as big shots... still 5-10 unique on targettted keywords are not et al... or is it?
I guess meta tags are imp but not very imp. The most imp tag after Title is description Tag. Keyword tag is just as a part of code. It dose not make much diffrence in Search engine results.
Like the rest of the team here, I would suggest you to put Title, Description and Keywords meta tag. Where Title tag should be put into high priority. Well, this is just what I do for my site for SEO and it works quite well for some sites