Virtualization and MySQL

So, the article at:
http://mysql-dba-journey.blogspot.com/2007/11/mysql-and-vmware.html says:
Don’t get seduced to the dark side unless you understand all the issues.
And that’s wonderful and all, but….what are all the issues? What are some of the issues? Is it related more to VMware, or more to MySQL, or more to MySQL on VMware? Is it something like “VMware isn’t stable” or more like “load testing on vmware isn’t always going to work because you won’t have full resources”?
Many people talk about using virtualization for development and testing….but if you develop and test on a virtual machine and then put it on a physical machine for production, isn’t that basically having differing environments for dev/testing and production, which is usually seen as bad? If a line of code crashes a virtual machine but is fine on production, is it worth tracking the bug down? How many hours will you spend doing that?
Also, how is using a virtual machine better/worse/different from using something like mysqld_multi on a machine with many IPs, or other strategies folks use in dev/test so they don’t have to buy the exact same hardware as in production, but still have the same separation of databases, etc?