There no any clarizen task integration with salesforce tasks (only milestones) Why?????. How you want to use chatter without this integration? Milestones is abstract items.
By the way. clarizen have not any integration with ms exchange tasks too. Sync process with salesforce looks like strange, not via push, only via scheduling sync! Once per day! You are joking? All this issues must be done yesterday. Look at your competitor "project cloud"! It's solution excellent for salesforce! Without any crutches like sync scheduling. update buttons and absent tasks in salesforce add on.