This page is regarding search engine exposure. It addresses whether a single domain or multiple domains is a better solution. Generally, branding one domain is better.. but having multiple domains (who may point to the branded domain) works best as a longer term more reliable solution.
For example, if you have some large website relating to wiki's, it's best that other people have the wiki installed on their domain too, incase one wiki goes down.
With regards to downloads:it's best to have mirror sites where you can download the same file. It's more work to maintain more domains, but if one site goes down and the file is deeply needed, what happens? If one site doesn't get indexed on the search engines, and it's the only site out there who offers the download, it won't be found.
Your best bet is to use multiple domains. Some domains may seem to work great for a while on the search engines, but then have problems for 2 years for no apparent reason. Some domains that are newly registered may work well, others won't. But it varies.
The reality is: it's unpredictable and not constant, whether your domain will perform well or not on search engines. So battle it with more variation. Get two or three domains.. but don't create mirror content sites. Rather create varied content sites with useful information.. i.e. archived mailing lists are someone duplicate content of something we've already seen before on other websites.. but are they useful? yes. Are they indexed by the search engines? yes.
The idea is mathematical:
The more variations you have out there, the better your chances. However, do not spend too much time on varying things, or you will not spend enough time on content.
Sometimes you may see an old geocities or tripod site ahead of sony.com for certain search term, or ahead of microsoft.com for a search term. I see many free websites that have good quality content too, though. It's not as if they are junk websites. This is because of variation.. it just so happens that some free websites can outperform real domain names..due to a number of factors. So the answer is not to use free sites for your future internet endeavors, just because they perform better in one situatoin. Rather it's just an example of how variation can improve exposure.. sometimes, a free site may rank higher on the search engine than a corporate site like sony or microsoft.
Figure out a system so that you can manage multiple domains, not just one. If one domain goes down, at least you have the other domain. If one domain doesn't get indexed by google for 6 months, most likely your second domain WILL get indexed within 1 month..
If all is going well for ONE domain, and then it gets pulled because your server screwed up all your 301 redirects, or because google just decided you only get 30 pages indexed this time and not 300.. at least you have a SECOND domain available as a backup, and hopefully a third one too.
If you can't manage two domains, then you have to reorganize your time or automate more things, or get a better server setup, or hire people.
Treat one domain as an "info only" domain if you can't handle high maintenence tasks on two domains. If all your domains are "info only" anyway, then it's not so hard. But if you sell things mechanically, and you mechanically answer phones, emails, etc. then it's best to keep one major domain name doing that work I think.Keep one domain as a "sales and info" domain. An "info only" domain is generally low mainenance because you don't have to respond to important things like email, orders, phonecalls etc. You just reference people to your main domain if they want to purchase something or sign up for your forum, or whatever you are doing.
If you don't think an "info only" domain would work, try an "archive domain", or something creative. Look at all the "archived mailing lists" out there. There are several mailing list archives out there who are just duplicating content legitimately. All these "secondary archives" of mailling lists always help me find information too. Because sometimes google doesn't get all the mail off the original site, but it grabs it from the second "mail archive" one.. due to variation, exposure, and chance.
Also think about the microsoft website.. A lot of people take articles off of MSDN and post them in web forums or post them on a website "this is from microsoft MSDN.. refer to microsoft.com if you want the entire article".
They have content all over the place that is not part of microsoft.com. People (legally) take msdn content and put it up on -their- pages saying "this is from microsoft". So if microsoft's website is down for a day, or google doesn't index that particular page.. it doesn't matter. They have -other- domain names out there doing work for them, and they didn't even ask these people to do this. If microsoft didn't get ALL of it's pages indexed on the search engines, chances are some -other website- who references microsoft WILL get indexed.
Same with affiliate programs.. look at all the affiliate programs out there who get multiple exposure with multiple domain names. Multiple domains are all promoting the same product. But each promotoer domain has slightly different content, due to variation of scripts, variation of the way human's quote things, etc.
If you can -get people to use their domains for your content- then that's good. (i.e. if you have affiliates working for you or if you have really good content that people reference). But most domain name owners will have to -do the work themselves- until they figure out ways to get other people to do the work. Ebay, for example, has people linking to their website through affiliate programs and web forums, just due to the fact that people like to buy products on ebay. Until you grow larger and people just start referencing your website everywhere, or until you grow larger and can handle something like an affiliate program, you have to do the multiple domain thing your self. It just increases exposure.. but don't do doorway pages.. do things like archives, secondary info, etc.