Maximum Number of Simultaneous Workflows

In a post here on SharePoint 2007 maximum limitations, Harshawardhan Chiplonkar - a member of the SharePoint Developer Support team - gave "workflows that can be run" as 15, clarifiying this by adding that this is the maximum number of simultaneous workflows that can be in memory executing code, not the number of workflow instances in progress in the database.

If 15 sounds like a small number for a "hard limit", you're not alone.

It looks like the 15 limit Harsh mentions might actually be the WorkflowEventDeliveryThrottle, which is 15 by default. This throttle can be modified (see below) - try setting it to a very low number, and you should see that workflow activation slows dramatically.

SPWebService spWebService = SPFarm.Local.Services.GetValue<SPWebService>();
spWebService.WorkflowEventDeliveryThrottle = 20; // default is 15
spWebService.Update();