VMware has quite a few features, but not all of them are ready for prime time. These are labeled as experimental, so at least the developer is forewarned. I attempted to install SCO UNIX Openserver 5.x, but it kept hanging. I did see messages in the VMware newsgroups claiming that some users had success with Sun Solaris 2.6 using VMware, so it appears that you will have varying degrees of success with each unsupported operating system. This provides an unlimited file system size for a particular guest operating system.
SCSI support is also experimental for raw disks and plain disks.
One of the best features of VMware is that it fully supports the undo concept. You can define, via your guest operating system configuration, which of the three modes you want to use. The first is just like a normal disk, with all changes being permanent. The second mode discards all changes at the end of the session, and the last mode gives you the option of keeping or discarding all of the changes made in a particular session. This is a powerful tool, since it can be used for all of the guest operating systems.