Delay page-validation until final submit so users can advance to next page

So how would the user correct their errors? How would an error be defined as "non-blocking"?

Webform doesn't have the ability to go to a particular page directly in the form. See these issues:

#335480: Set separate URL for each page of Multi-Page Forms (Funnel Tracking)
#258696: Multipage form - Page n of n (progress or percentage complete)

At this point there are so many technical reasons why we wouldn't do this I don't think there is much reason to keep this issue open.

quicksketch is quite right about this being a non-trivial server-side change within the module, but you'd possibly be able to achieve something like the effect you require by making use of css and jquery, i.e. set up the form as a single page, group your "pages" into fieldsets, set all the fieldsets except the first one to display: none; onclick of submit button hide the current fieldset and show the next one via javascript (change the button text, display error messages etc via javascript).

You may need to conditionally include the css file that does the hiding of fieldsets only when form is loaded for the first time to be sure that users can see the Webform generated errors and highlighted fields when the form redisplays. Experimentation will be your best guide.