How often does Marketo sync with salesforce?

I was told every 6-7 minutes.

I think its different for every person. I myself find myself asking myself the very same question. Sometimes I have to wait 2-3 mins for something to sync / back-sync. Other times I've had to wait over 20. 

Suppose you create a campaign in SFDC and are waiting for it to sync back to marketo, I"ve had occasions where it hadn't synced for over 2-3 hours!