Here is a great interesting take on the “Long Tail” written by Dustin Woodard, guesting on Hitwise.
SEO for recruitment keywords is massively dependant on company size and how niche that company is. For example, if your recruitment company hires advertising staff in London, I’d suggest that’s not very niche, so realistic goal setting in keyword analysis would be to look at what is niche – for example – basing more keywords on what your clients themselves do (“TV Advertising specialists”); focusing in on ‘tighter’ locations (“Walthamstowe Advertising Jobs”), etc is the first start. Let’s not run before we can walk. If, however, your company is already niche – such as a recruitment company specialising in recruiting antique furniture restoration staff (for a pretty rubbish example), you’ve already covered many of your keywords (we hope!) by the time Google starts crawling the jobs themselves.
From looking at our clients analytics, the tail can be pretty long, – I’d guess that the best conversions come at about any four-word phrases.