Certainly steww, offering professional seo services where you expect to keep clients for a relatively long period of time is all about managing expectations. Its striking the balance between explaining the reality of it to them i.e. no amazing results "overnight", but at the same time not dampening their spirits too much where they think its too much hassle.
Blossom, I agree with the first paragraph above, but from experience with some of my own sites there is such a difference in being on Page 1 and Page 2 on Google, really you want to be in the top 5 results on Page 1.(I know you didn't say anything about being on Page 2, but I'm just saying that being number 11 instead of number 5 for a search term means your traffic may receive only 10% or less of the traffic that you would receive if you were in the top 5.) One of my sites is on page 2 out of about 150,000,000 results for a search term that gets 2000-3000 searches per month, but only receives circa 50 visitors a month for that given keyword, whereas the sites in the top 5 of Page 1 will probably be getting 1000 visitors per month each, just for that search term.
Although it looks encouraging for a client's site to come from 'nothing' to Page 2, in reality they need to be on Page 1 for any search term, unless like you said its getting a very high volume of searches per month, in which case it is usually a huge amount of SEO work over a longer period.