You know what I am talking about, "In order to show you the most relevant results, we have omitted some entries very similar to the 1 already displayed. If you like, you can repeat the search with the omitted results included."
It frequently happens to sites that are dynamic in nature, and when you do an allinurl:www.site.com site:www.site.com query in Google.
What you should normally watch out for is having the top content that is the same for each page. With CSS-P (cascading style sheets positioning) you can force the real content to the top of the page and ensure that Google reads that content first. That will help prove to Google that your page is not similar to the other results.
A thread at WebmasterWorld is currently discussing this topic.