Closed source is a mistake for VMWare.
My company currently uses VMWare and have no problem paying for support from VMWare but open source is important to our strategy. If VMWare has not opened it's source before an open source competitor gets good enough for our needs then we'll be switching to the open sourced competition. It's not about the money, it's about the freedom and the guarentee that we have control of our business.
We require the stability and speed of VMWare, hosting on Linux, support for hosting at least Linux, BSD, and Windows without any OS patches, live backups, and clustering with live migration. When Xen on another open source product can offer these I'll switch and sign a support contract with them.