An SEO Chat thread discusses the caching frequency of the MSN Search Engine. Basically, how often does MSN re-cache your page in the index.
My corporate site was last cached by MSN on 6/4/2005, this blog was last cached by MSN on 6/13/2005. So like any good search engine, MSN has different caching frequencies based on the frequency the site is updated by the webmaster.
This complies with the reports in the SEO Chat thread of individuals reporting 3 weeks, 2 weeks and even 3 day re-caching frequencies by MSN Bot.