I'm experimenting on subdomains at the moment. It seems they get traffic just as well as a normal domain. it may be a disadvantage when you try to submit your site to directories, because most webdirectory won't accept subdomains.

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I aLook at amazon.com! They have thousands of keywords and they still use 1 domain, but why? It is not because a huge site "weighs" more - it is because it does not really pay off to have more domains than 1, provided the theme of keywords is the same. If you have a sub-domain you would think because you would have the domain name like [keyword].[domain].com it would rank better but it does not because the SEs see that as a completely different domain and they check if they have the same IP address! To overcome this you would have to register with different hosting companies (you would then get different IPs). This is a lot of work and more cost and it just does not balance out if you just go the easy way of having a sub directory (which has your keywords enclosed). I would go for [www].[my domain with main keywords].com/[my category]/[my product or keyword]. If you want to have this pages ranked at the top of Google you need to provide link juice with keyword rich links to it (high PR). That works best. Hope this answers your question and saves you a lot of work and cost. liver