It shouldn't have any effect since Google views subdomains as separate entities. This is why it's better to have your company blog at www.domain.com/blog as opposed to blog.domain.com. Getting a lot of links to blog.domain.com doesn't help www.domain.com.
I was aware of that with Google (at present) but am not sure of the situation with Bing (or others) - that's why I asked, kinda.
I thought jacquesm might be ahead of the curve on something here or that he knew some trick for multiple category ranking or something.
I'd also imagine that it increases the instantaneous value of the domain from a sale perspective as a wider range of pages can be presented in the SERPs on a domain that has many subdomains if some subdomain is relevant to a particular search alongside the main domain.
Was just a thought really, thanks to jacquesm for answering.
