I created a timestamp field in Salesforce that Marketo updates when a lead hits MQL via a trigger smart campaign, and then I run a report on that field at the end of the month. Do this for all lead statuses you want to report.
Like Jason, we have an MQL date field on leads. When they are converted to SQLs there is a separate date field for that, too.
We report qualifed leads to sales using the RCA. Our success path is created such that we have an SLA off of our success path for our "suspects" which are marketing leads directly pushed to sales. They have 14 days to change the status of these leads. Setting up our success path in this manner makes it super easy to pull a report to see who has/hasn't moved from there.
You can then also pull coinciding SFDC reports for Sales Managers to have insight as to who has/hasn't moved along the success path, which we've found extremely helpful.
I tried RCA and success path and doesnt work for us.
We have a date stamp on the Salesforce side as well but this doesnt help in this case because a lead could MQL, then become recycle, and MQL again but the stamp doesnt update. I need to see what leads were generated - new or existing - and what sales is doing with them.