At my work, I use virtualization software extensively for various reasons. I have virtual machines with ESRI software that I use for testing purposes, for example, when installing newer software versions like ArcGIS Desktop 9.4 (now is renamed to ArcGIS Desktop 10). Sometimes it might be very good to have several copies of the same virtual machine, i.e., identical clones, which can be very useful when experimenting with operating system settings. Moreover, it is very convenient to share a virtual machine with a colleague so he/she could take a look at it and help to fix a problem. As far as I know, many companies (Microsoft, Oracle, and IBM just to mention a few) use virtualization techniques to distribute installed and configured software to their clients. In those cases a client has an access to a ftp-server and everything one has to do is to copy a folder with virtual machine files to a local server. I used to use VMware for about 5 years and I like it very much. The software interface is very intuitive, documentation is very well written, and there is a big user community. Of course there are nice free alternatives like VirtualBox (which I can recommend highly for desktop virtualization, but of course only couple of vendors provide tools for really enterprise level support). Recently, while working with an old virtual machine I had for a long time ago, I realized that its disc space was not sufficient. Thus, I was in need of extending the virtual disk size. After searching on Google for a while, dozens of suggested methods have been found. Most of them, however, were not very straightforward and quite often worked not as many users did expect (as displeased user comments testified!).
An elegant and free solution is actually provided directly by the vendor. The utility is called VMware vCenter Converter and is available for download from the VMware web site. It worked fine to me; to extend a virtual machine disk of 10GB to 15GB around 1 hour was required. Nevertheless, it is the best solution I have seen so far. This is really a must have utility for any person who use VMware machines extensively in day-to-day work.