onsip.com is the marketing site for OnSIP, our hosted VoIP phone system for small to medium sized businesses. Our main aim with the site is to inform, inform, inform -- the technology is still in its adoption phase so there is still a lot of confusion about what it is, what it does, and how to implement it successfully. Much of our site focuses on driving the message home about our core business so that potential signups have all the tools they need to decide for themselves if it suits them; business VoIP is by a no means a one-size fits all kind of thing and we try to make that clear.
We mainly use drupal because if we want to do something, chances are that we can - and easily, too. Probably our favorite part of the entire experience with drupal was using the zen starting theme, which lets us customize any aspect of the theme we wanted with relatively low barrier to entry and near limitless possibilities. The fact that the zen theme is so nice definitely speaks volumes about the drupal theme design.
We also use the book module to maintain an ongoing database about everything one might want to know about our business / tech support queries / phone compatability guides/ etc. Our 'knowledgebase' is regularly updated and located on our sister site, junctionnetworks.com.
Drupal makes it easy to maintain our own little encyclopedia, and structure it like a Wikipedia article. It's also especially easy for any user on our site to add content that's correctly formatted without having to worry about the CSS. All it takes is a little Javascript and h2 - h6 tags can be used to format and organize instructional articles. Example here : Configuring Bria Softphone .