[eluser]Nick Husher[/eluser]
+1 Colin Williams: Use DIV and SPAN tags rather than contort the semantic meanings of other tags. Use fieldsets to group semantically-similar fields, using nested fieldsets where appropriate.
It would be reasonable to have elements within an ordered list if you expect the form to be filled out in a set series of steps, although the case is less clear for an unordered list when you could use a semantically-neutral collection of div/span nodes.
