I'm new to Piazza, but found it to be a great way for not only reducing workload (less email), but students get help faster, and what I like best of all --- students helping students!
This is the first semester I used Piazza, and it has been great. I used to use a class mailing list, which worked well, but Piazza takes it one step further. I can't think of anything I dislike about Piazza, you've done a great job!
Piazza has figured out the right user interface for doing online discussions for a course. Students really participate, and it's easy for me as a faculty member. It's surprising how much better it works in practice than a discussion forum that is part of a big multi-purpose course management system.
Instructors can create a Piazza for their class with a single click.
Students and instructors are automatically enrolled with appropriate roles, based on the course roster.
When clicking on Piazza in Blackboard, users are automatically signed in to Piazza, so there's no need to remember a separate user name and password.