I have seen the power of internal linking with Wikipedia pages, so I am wondering hwo much is too much? Wiki has sometimes up to 100 links on one page and I am wondering if they get a pass? Is there density to how much internal links you can have on your page?
No there is not such thing as "too much", but for good results in first place you should follow the google recommendation "not more than 100 links on a single page". I know and have seen that some sites do have a certain success violating this recommendation, it's not the rule but the exception. You can do a complete linking on your site (every page links to every page) and it "won't hurt your rankings"! This is a very relative statement that's not describing the truth totally, "won't hurt your rankings" is not the exact term, it means you won't trigger a filter or get penalized for doing so. On the other hand, a smart internal linking structure can do much, much more for your site than a complete interlinking of all your site's pages and sometimes even more than 1000s of one way links from other sites..
WIKI is a great example of internal linking down right. They link within the content of the page. Google, and other search engines, love it. I always recommend to my clients and as best practice with my employees, to link within the content of your own articles to internal pieces. It helps tremendously and really spreads the "link juice" evenly throughout the whole site.
The 100 links per page is a google "recommendation", not a rule. There are many sites that break this all the time and have very high PR. A properly designed "breadcrumb" will do the same as Wiki. I also have tested this very scenario. Clean top-down navigation and "all-links on all pages". Google will see all the pages at the same time, but the PR calculations of the "all links" was 4 to 1 faster. Just keep the link looking clean and user friendly. I'm at about 45 to 50 links per page and everything is ok (2 1/2 years). Remember, 100 links on a page looks bad.