How to define SEO targets

[Param]

During my work <snip> I am often asked how much time will the SEO take in propelling a particular keyword to the top 10 rankings in Google.

I understand that it depends on competition and the popularity of the keyword and the required time can be highly variable but is there any particular mechanism through which such targets can be roughly defined. Help is deeply appreciated.

[edited by: Receptional_Andy at 4:55 pm (utc) on May 11, 2009]
[edit reason] No specifics please, see charter [/edit]

[AnkitMaheshwari]

Traffic is always a better measurement tool than rankings.

[bilalseo]

keywords selection, traffic estimates, trageted audience, on page seo factors, off page seo factors, etc...

[idolw]

Traffic is what brings money, not positions.

[LifeinAsia]

how much time will the SEO take in propelling a particular keyword to the top 10 rankings in Google.

How much time until you make your next million dollars? How much time until the human race dies out? Too many variables to answer.