I have a client that has (honestly) over a hundred web sites with the same page content. Dynamically generated, their sites are about 4500-5000 pages. The sites aren't absolutely identical - they have somewhat unique headers and footers, unique graphics, navigation and advertising columns.

Surprisingly, every page on every single one of their web sites gets indexed in all the major search engines. Their SE placement for many desired keywords isn't great - pretty hit and miss. Sometimes outstanding, sometimes poor. But the reason for so-so placement is probably that they've fallen behind current SE trends and they have a _lot_ of room for improvement with respect to simple optimization.

They've recently hired a SEO firm.

First advice from the SEO folks: Get rid of all but one web site. Duplicate content penalties are killing you.

But, are they truly being penalized for duplicate content? How can you really say this when some of the pages score first page hits for some search keywords? And if a SE detects duplicate content wouldn't it just _exclude_ the page from its index?

Without knowing too much else on the exact details on the sites, there's a good chance that they keyword phrases are not overly too competitive, and focusing all their efforts onto one big site, with ongoing link building and continued content building, they will be able to reach their goal of the top keyword phrases in their industry.

As you mentioned below.

Their SE placement for many desired keywords isn't great - pretty hit and miss

Picking one site will ensure that they will not jeopardize losing the majority of their rankings/sites in the search engine from spamming . It is working now, but there is always that chance that someone will catch on and report it as spam, or the search engines will find out for themselves.

If this was my business, I would rather have a site that is long term and stable. It takes time to get a site ranking for the top keywords in their industry and this will help with greater gains in sales and leads. It seems (without knowing too much on their site/business) that relatively anyone would be able to come in at that same level and take a lot of his business away.

You would almost need a long term plan (or a 12 step get me off spamming program) to make the switch over for all the sites. Check the logs/stats and find out all the keywords they are ranking for, and overtime work them towards the main site. You'll need to have a nice laid out plan to show your client so they can see the benefits of making this switch.