Had a conversation about sitemaps with someone from marketing. It was stated that a single page shouldn't have more than 100 links because Google will not follow more than 100 when crawling pages. I had not heard of this limit before.
I did some searching and found that Google's Webmaster Guidelines used to state "keep the links on a given page to a reasonable number (fewer than 100)." [2008] The Google Webmaster Guidelines now just state "keep the links on a given page to a reasonable number."
When engineering a sitemap architecture for a site of say 1,000 pages (or link list on any page for that matter) would it be acceptable to place all 1,000 links on a single sitemap page or should multiple sitemaps be used?
Also, does submitting an XML sitemap nullify the importance of an HTML sitemap to Google's spider? If so, then I would imagine only placing important links on the HTML sitemap instead of a link to every page to tailor the page to end-user usuability.
Depends on whether you're referring to sitemaps targeted towards users (which is what @adrian-k answered about) or sitemaps targeted towards robots (i.e. search engines).
If it's the second kind, then the answer is: you can (probably should) have several thousand links per page. It also pays to make life easier on your crawlers by including 'lastmod' values for your pages and by gzipping the page itself.
For information on valid formats for such sitemaps see http://www.sitemaps.org/protocol.php
Just to validate, take a look at what the big boys are doing. In most cases you'll find a reference to the sitemap page at the bottom of /robots.txt. For instance, http://www.linkedin.com/robots.txt or https://profiles.google.com/robots.txt
LinkedIn's sitemap, at http://partner.linkedin.com/sitemaps/smindex.xml.gz, lists another 2630 gzipped mini-sitemaps: curl http://partner.linkedin.com/sitemaps/smindex.xml.gz | gunzip | wc -l.
Google's lists 7104 such pages on their Google Profiles sitemap (http://www.gstatic.com/s2/sitemaps/profiles-sitemap.xml) - curl http://www.gstatic.com/s2/sitemaps/profiles-sitemap.xml | grep '<loc>' | wc -l
Play around websites of SEO-aware members of your industry and you should find some more examples (or discover that you can beat them hands-down with this knowledge).