Extension vs extension-less link set-up

Pros and cons of either approach

[Tastatura]

Hi all,
I am in the process of building a site, and am currently tackling organizational and technical issues. One of the things that I am pondering is how to set up links, or more specifically should I go with extension or extension-less links to pages.
Example:
‘Extension’ links : Mysite.com/topic1/page.html or
‘Extension-less’ links : Mysite/topic1/page

What are pros and cons of either approach? For example, ‘extension-less’ approach might place additional load on the server (due to content negotiation or mod_rewrite), however it doesn’t revel technology behind delivery of the page (hence if in future delivery tech is changed, links do not have to change – although with few tricks ‘extension’ approach could do the same). However, it can be argued that most user are accustomed of seeing an extension (perhaps mostly *.html) to know that they are looking at the page. With “extension-less” approach, it could be confusing to discern if you are looking at the page or directory.
I am looking for some input about any pros and cons for either approach.
Thanks

[tombola]

Tim Berners-Lee provides good reasons to use content negotiation in this article:

Cool URIs don't change [w3.org]