I know that all web-to-lead forms for Salesforce should really become Marketo forms instead. We will do that. However, the AppExchange sends leads to Salesforce ISVs directly through web-to-lead and that's the only option.
We currently use Auto Response Rules in Salesforce to send an email back to the person. This is a natural fit for Marketo to replace.
My main question is regarding sync frequency. Imagine a person being on AppExchange and completing a form there. It goes to our Salesforce org, syncs to Marketo to get sent and Marketo sends the email. The person completing the form on AppExchange will not get the response until after the sync.
When new leads are added to Salesforce, how quickly to they make their way to Marketo? How about the related Custom Objects? Is it immediate, every x minutes or every x hours?