In Incognito mode, cookies are discarded at the end of your browsing session, so this makes it less likely that users will be identified.
If a user clicks through their email in incognito mode, or copy-pastes a rewritten url from an email into a browser in incognito mode, they will be cookied. The cookie will not be saved when they exit incognito though.
If a user logs in and browses or purchases, they will be identified.
If they aren't identified, interests and pageviews wouldn't be attributed to that user, but pageviews would be collected against the items of content, so while items would continue to gain popularity, the interest profile for the incognito user would not be built.
For sites using Site Personalization Manager, any user-profile-based personalization would rely on the user being identified, so they may not see tailored content. Collaborative filtering based recommendations would work as normal.