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It depends in part on what you mean by "pointing". "Pointing" generally refers to allowing other domains to display the same content as the site they are pointing to, under their own domain, e.g., so ExampleB.com would display the same content as ExampleA.com. That is one kind of duplication that may get you in some trouble with the algo's.
If you are talking instead about redirecting those secondary domains (preferably with a 301) to the main site, in order to pick up the type-in traffic from those secondary domains, no real issue there.
For example, i would buy hxxp://widgets.com which would be redirected to land on the page on my site about widgets. Right now, the address of my page about widgets is hxxp://mymainsite.com/widgets.html
Will having related sites place links to my widgets page using the keyword rich domain name hxxp://widgets.com redirected to my widgets page help my rankings in yahoo?
I'm also concerned that i might get caught in a duplicates filter being as hxxp://widgets.com and hxxp://mymainsite.com/widgets.html both point to the same page. Will this be considered as spam by search engines?
Bear with me, as i'm new at this. My competition built 15 different related sites listed under webmaster aliases to place links back to his main website to get in the top serps and it's working well for him. I'm trying to avoid blackhat seo like that though.
[edited by: caveman at 1:20 am (utc) on Oct. 16, 2008]
[edit reason] For clarity. Tip: Use paragraphs. ;-) [/edit]