Google uses Open Directory Project (DMOZ.org), to power its directory. Coupling that fact with the observation that sites listed in DMOZ often get decent and inexplicable PageRank boosts, has lead many to conclude that Google gives a special bonus to sites listed in DMOZ. This is simply not true.
The only bonus gained from being in DMOZ is the same bonus a site would achieve from being linked to by any other site. However, DMOZ data is used by hundreds of sites. The biggest user of DMOZ data is Google, but it is also used by hundreds of other sites. The links from these sites are often too weak to be listed in a link search, but Google does crawl them, and the links do count. So if you're listed in DMOZ, you're actually gaining the benefits of hundreds of lightly-weighted incoming links, and when you add all those up, the total can amount to a decent PageRank boost.
There are two other benefits you can gain by being listed in DMOZ. For one, your directory description will appear with Google search result listings, which may increase the likelihood of someone clicking on your link. The other benefit is that, as Google does crawl DMOZ, being listed there will ensure that you're also listed in Google. However, as it's so easy to be listed in Google, this benefit is slight at best.
This myth evolved much in the same was as Myth #5. Google has been partnered with Yahoo! for a number of years by providing secondary search results, and just recently (Fall, 2002), Yahoo! started using Google to provide primary search results.
Because Yahoo! uses Google, many have assumed that Google also uses Yahoo!, which is not the case. The only PageRank you will gain from being listed in Yahoo! is the same as the PR you'd gain from any other site of equivalent weight. However, some people achieve a larger-than-normal boost from their listing in Yahoo!, which again leads to this incorrect conclusion.
The fact is that being listed in Yahoo!'s main directory will often get you into regional directories, so, much like DMOZ, one Yahoo! listing can result in multiple links. These links are often weak in nature so they may not show up in a link search, but they are there -- and Google knows about them.
Additionally, once you're listed in any search engine or directory you have an increased chance of someone finding your site, liking it, and adding a link to it from their own site. As such, being listed in Yahoo! could result in you receiving links from elsewhere -- links whose weight is too low to list, but which do contribute to your PageRank.
This myth is left over from the days when most search engines used meta tags. However, Google has never used them. This fact may be contested by some people, so I wouldn't post it without proof.
To prove to yourself that Google doesn't use meta tags, put words into your meta tags that do not appear elsewhere on your page. Then, using an advanced search, search for those words while limiting the results to your domain only. You can try this on any search engine -- and if results appear, you'll know that engine uses meta tags. If no results are displayed, then you know meta tags are not used. It is important, though, that the words only appear in your meta tags and no where else on your page.
Some misguided people, mostly amateur search engine optimizers, may claim that Google still uses meta tags despite this test. Mostly they believe that meta tags only work when they mirror the content of the page itself. This is similar to what is known in psychology as a self-confirming delusion (an imaginary friend only you can see) because it is impossible to test with a single page. With multiple pages you can test it though and in this article I provide conclusive evidence that Google does not use meta tags, even when they mirror the content of the page. Amateur hacks take note.
Google can sometimes use the meta description tag to create an abstract for your site, so it may be useful to you if your home page is primarily composed of graphics. However, do not expect it to increase your rank.