We have ~ 20,000 contacts in Pardot and have Salesforce integrated. We are looking to do more integrations with Salesforce and Pardot.
1) Import custom fields from Salesforce to Pardot.
2) Import both Lead and Opportunity Contacts to Salesforce and have the two systems integrated where each one updated the other system.
3) Automatically update lists with segments based on values in custom fields.
This is less Salesforce work and more Pardot work, so only apply if you've also worked in Pardot.