It's nice to see a growth spurt here recently at WmW.
>>>>If I map two domain names to the same site... and submit both domain names to the search engines, how do search engines treat such listings ? Won't they "notice" its a duplicate of content and penalize the listings somehow ?
The nature of this question is quite plainly more about ethics than about technicalities.
Sure you can use some well known tricks and redirect the visitors to one domain. And yes some engines will pick up dupes (AV) and others (Google) won't be so sensitive.
The more I learn about this stuff (seo)...the less I feel the need to use "tactics". I believe the reason for this is that I am becoming more adept at producing a quality web site to start with thereby reducing the need to augment my efforts with other methods with questionable ethical implications.
I believe if you do the keyword research, pick the right domain name, use a theme site directory structure and start a linking campaign on top of basic, quality seo methods....I think you have done 99.9% of what it takes to have a good shot at a high ranking.
Yes, some of the doorway techniques still work. Yes, some of the redirection methods still work.
Take a good hard look at the theme directory structure that BT laid out a couple of weeks ago. You know what I see...built in doorways that won't be considered doorways. Hallways that are integral in the site structure. Integrity in the entire scope and topical essence of the keywords you are optimizing for. I don't think this type of thinking will fail anybody in their efforts to succeed.