We've been using it for a while now, through version 5 to 6.5. I mainly use the SAS side of it (Server Automation System). There are a number of different components to Opsware, that are very different depending on the version you use.
Currently we use it to manage, monitor and audit servers, there are over 3000 servers that Opsware manages for us without any issue. We also use it for software deployment and registration.
Opsware has recently been bought by HP and is now integrated into it's Data Center Automation Center suite. The following link contains information and white papaers for their suite, which includes the Opsware products.
https://h10078.www1.hp.com/cda/hpms/display/main/hpms_content.jsp?zn=bto&cp=1-11-271-273_4000_100__
Personally, I find Opsware very usable and useful. It has saved a lot of time in the management and deployment of software, server provisioning and patch management.