I've been looking into how best to optimise the search engine results position for a local company called Bell Leisure. They have two quite distinct sides to their business: one half is selling pool and snooker tables, and anything related, and the other half sells, installs, and maintains swimming pools and hot tubs.
Their current site is all under the single www.bell-leisure.com domain, with two sub-directories for the two halves of the business. The effect seems to be that their site is listed well in pool and snooker table categories, and also appears well in search results for these types of product. However the swimming pool side of the business doesn't appear well in search results, presumably because it doesn't fit within the categorisation of the site as a whole.
If the company agrees, I'm going to try splitting the site into two separate sub-domains, one for each distinct part of their business.
So http://www.bell-leisure.com/swimming will move to http://swimming.bell-leisure.com, and http://www.bell-leisure.com/tables will move to http://tables.bell-leisure.com. I'll leave the existing "home" page at http://www.bell-leisure.com, and will put in permanent re-directs for the other pages, so previously-created links will still work.