Thanks to Jesus this is our 14th year in business; and through many of those years we've been using Cerberus.
Thus stated, in our case we are looking at moving away from Cerberus for several reasons:
1. We are having issues receiving email from clients sending through Microsoft Exchange Server. While we are on an older, paid, version of Cerberus, looking at Cerberus forum posts, we see that this appears to be an issue with others as well (even on newer versions).
2. While we've considered upgrading to the latest Cerberus version, we find it extremely cumbersome and anti-user. That's just our take.
I know there will be positive responses for Cerberus; and that's a great thing as it does work for various parties... it just started failing miserably for us.
I know cerberus has issues retrieving emails from Exchange 2007 servers which kind of sucks if you running it in a Windows environment, but overall Cerberus has pretty nifty features and is very effective when tracking work that needs to be done.
What impressed me as I was doing research yesterday (we need to leave Cerberus as quickly as we can, but not so fast we miss something) was the power of HelpSpot's API.
People are using the API for tying in with various CRM systems, email contact managers, and what not.
P.S. We do currently use Cerberus to manage multiple companies; but as I stated, it chokes on email from clients using Microsoft Exchange Server. So if you will never support any clients using Microsoft Exchange OR you can command those clients to drop Exchange...