Despite everything said about link farms, people actually engage in them without being truly aware of it. The fact is, linking IS important. Linking and content alone will probably do more work than rigorous scientific techniques and automated methods. But it can be dangerous to get overly attached to linking and not know that indiscriminately linking (reciprocally) to a link farm can get you grey listed and banished from Google's SERPs until you come humbly clean (give them a few months before you get relisted).
Link farms won't come up and tell you "hey, I am a link farm and just have thousands of links to totally unrelated sites." Instead, you'll get an offer from a third party site or via email. You have a responsibility to check that you are not linking to some link farm; you can't control who links to you. If you are linking to a banned site, your site may be penalized. Some people even network and set up link farms; a network of full-time housewives once linked to each other and unintentionally created a perfect link farm. Please note: SEO firms check all sites linking to you on a monthly basis; that's one reason why they collect a maintenance fee.
Myth Two: Multiple Domain Names Pointing to the Same Site Increase Rankings
If you have multiple domain names pointing to the same site, the search engines call them "mirrors" and will penalize you (the mirrors won't get listed). So if you have multiple domain names and you want to remain in the SERPs, build sites to correspond to each separate domain name.
If the sites look like doorways you can also get penalized. There is, however, an increasingly thin line between "micro sites" and "doorway" pages. If you create a mini-site to funnel traffic, endeavor to get some content on it.
If you insist on tying multiple URLs to a single location despite my educated opinion, strive to keep your multiple domain names to less than ten. You should ideally stay with subdomains to funnel traffic to your targeted pages (the rule on the Internet is that a page is a page is a page). You don't need multiple domains and they don't work, unless you have content-rich micro sites. Search engines are run by people, and people don't enjoy been manipulated.
Myth Three: Resubmitting Your URL Repeatedly to Search Engines
I don't submit URLs to major search engines; I only submit them to niche sites that would take forever to index a URL if it is not submitted. Sometimes when you submit a URL it takes a very long time before it is listed. It is okay to submit a URL once; resubmitting it does not make sense. In fact, according to some websites, it could even affect the submitted page adversely. That is hearsay; however, submitting a URL multiple times does not affect rankings positively. Submitting your site in itself is also totally useless if the site is not search engine friendly.
Joke Break
Here are a few myths that are truly hilarious (and hopefully are just jokes). I found them on various threads and discussion boards across the net, especially here.
Google hates me.
The only search engine is Google.
There are a million search engines.
AdWords are moving to the left of the screen.
You won't get caught for spam.
Matt Cutts hates me.
All SEO wear hats.
Matt Cutts is leaving for MSN.
People on SEO forums actually ALL know SEO.
Hidden text works.
Black hat SEO and White hat SEO are easily distinguishable.
SEO guarantees number one ranking.
SEO is rocket science.
SEO doesn't take time.
My competition hates me (okay, that may not be a myth).
Concluding
There are a few other myths, especially concerning professionals, the tools they use to optimize, and the search engines themselves. These myths are spread by pseudo experts and some other SEO "experts." Hopefully with time we will cover some more myths that have not been treated on SEO Chat before.
Search Optimization 
