Server based computing started in the mid 90's.
I was involved in a number of successful projects and saw how organisations benefitted from centralising support and enabling remote working.
Server based computing continues today as a valid method of centralised desktop delivery, however organisations are more keen to deliver a full virtual desktop, rather than a shared desktop, i.
e.
each user also has their own copy of Windows XP / 7, rather than sharing a server operating system.
Running a copy of Windows for everyone presented the VDI vendors with a challenge - how to design an affordable solution that could run multiple copies of a desktop OS in the data centre.
The initial solutions were designed for the enterprise, complex and costly, including many storage area networks (SAN's) and multiple management servers.
The benefits of VDI are significant, but the upfront costs of simply piloting an enterprise VDI solution were too much for small to medium organisations and many smaller schools.
Therefore the initial VDI solutions were in many cases too costly and too complex for mass adoption by the SME market place.
However, some of the mainstream vendors have realized this and doing something about it.
There are now VDI solutions that can work well for the SME market place, typically suiting organisations with between 50-1000 desktops.
The vendors have cleverly removed the need for expensive SAN's and complex management server configurations and packaged all the components needed to deliver VDI into an all in one software product.
This has enabled organisations to start with a handful of users and add more as and when required.
In fact the new VDI solutions can work out cheaper than buying new PCs and can help SME organisations to benefit from:

• Improved support - no need to travel to the desktop
• Reduced desktop refresh costs - extend the life of your PCs
• Workforce agility - enable staff to connect from any device and any location, securely
• Simple Windows 7 deployments - upgrade one image rather than every PC
• Improved security - prevent staff from storing data on devices and remove the need for memory sticks

The time is therefore right to look again at VDI and see how you can start to create real business benefits for your organisation.
You should also consider replacing failing PCs with thin clients if you have a VDI environment as this can extend the benefits of VDI and further reduce your operating costs.