We have had a scenario where Marketo/Salesforce integration caused a spike in API useage. This went to 90% of the allowed Salesforce API limits for our organisation.
Going forward this same transactions could exceed the limit in Salesforce and cause Marketo but more importantly other APIs to stop working.
Backupify has a great feature that enables an System Administrator to define how many (Salesforce) API calls it uses on a daily basis. And based on this stops any additional API calls from being made to Salesforce in a 24 hour period. In addition when this limit is reached it alerts (via email) the System Administrator who can increase the limits if they feel safe to do so without impacting other applications. Once the limits are available Backupify would continue it's sync where it left off.
This feature would be great to prevent Marketo accidently exceeding Salesforce API limits.
The alternative is to set up threshold reporting within Salesforce (which we have) and if the limits are reached to 'Freeze' the Marketo account or disable the Salesforce Sync from with Marketo (then remember to unfreeze/enable) when thresholds reduce.