Can the same Marketo tracking code be used on more than one web property. If it can, what are the pros and cons?
You can...technically. What are you trying to do? There are several threads on this topic.
Pro: View activities across all your websites for your leads. Action based on interest in different product lines with their own microsites.
Con: None in most cases. Heavily loaded Mkto instances will not like more traffic, but this is getting better.
Caveats: Activities are anonymous on a given domain until a lead is known on that domain. Significant development is necessary to skip that requirement.