[SEO] Domains with keywords

Hey,

I'm looking for some insight into buying domains with good keywords/phrases in them for projects. I've heard that if you have a domain with an exact key-phrase that someone searches, you are more likely to be higher up the SE's for that key-phrase. Is that correct?

So, for example, if you want to sell peanut butter to people, a good key-phrase that people would search is "buy peanut butter". If you have buypeanutbutter.com as your domain, are you more likely to be higher on a SE for having that key-phrase in that domain?

The reason I ask is because I am looking at the possibility of purchasing a second domain for a project I am launching, which would be another good key-phrase alongside the project's main domain. My second query is whether it is a good idea to have multiple (well, say 2 or 3) domains which are really good key-phrases for your project and use the same zone records, so depending on which keywords/phrases someone searches, they land up on the same site, but it might be on a different domain (but the domains would all mimic the same website, so there would be no difference depending on which domain you land on). Hope that makes sense.

So in the peanut butter example, some other good key-phrases alongside the main buypeanutbutter.com could be purchasepeanutbutter.com and peanutbutterforsale.com. So by having all three domains with the same zone records, would you overall improve the chances of people landing on your site via a Search Engine?

Thanks