We utilize the MPLS WAN service to connect almost two dozen sites and nearly 300 users, back-hauling everything to our corporate office. We also connect in our Disaster Recovery site.
Utilizing Ethernet and T1 lines the service is fairly reliable and simplifies the handling of traffic.
The downside is there is often an extended period of time waiting to talk to customer support, typically 30 minutes to talk to a person then waiting for a callback on the generated ticket which can take hours or more.
We've also had issues with getting access to their customer portal.