My users are having issues since the 4.x upgrade where they click to reply to a post or create a new topic and 30 seconds will pass before the action completes.  I didn't have this issue on 3.x and my server resource utilization is very low.

Is there a setting or something I should look into?

Normally when it takes exactly 30 seconds, its something related to email problems.

Send a test email and check if it works. 

Ok, just sent a test email, took less than 1 second and I received the email.

Show the processes in phpmyadmin on a refresh during a post and see what's holding things up. 

As in watch this list and have them post?  Not exactly sure what I'm looking at here.

 

Yeah, click on the <-- T --> to expand all the queries. Set it to auto-refresh and then watch what happens when a post is made. If you see a lot of processes queuing up saying "waiting for table lock on xxxx" or spending 30 seconds creating a .tmp file then you have something to investigate.