If the idea of virtual servers scrambles your brain then try thinking about this analogy. Suppose you need a PA in your business. You could either employ a real PA in your business OR you could rent the time from a virtual PA working in a call-centre. When the virtual PA isn't answering the phone for you, he or she may be answering the phone for another company helping you with their costs. Equally, if your virtual PA goes off sick, their work can be done by a colleague very easily - with much less hassle than if your employed PA went off and you had to find a replacement.
So... (a) sharing a real person's time is analogous to a virtual server sharing a real PC and
(b) switching to another virtual PA is the same as switching virtual servers if the original one has a problem (easier backup!).
All good? Not necessarily. Suppose you contract with The Virtual PA Company but you are not happy with their work - they take too long to answer the phone. So you switch companies to Virtual PAs R Us as they seem to offer a better service. Without realising it, you find that Virtual PAs R Us are actually using the same people to answer the phones - so you get the same bad performance as the service is actually provided by the same people!
This happens with virtual servers too - sometimes performance is poor and IT server staff adjust resources on the virtual servers to try to increase performance. However... if the physical boxes hosting the virtual ones are underpowered or over-committed then the virtual servers will always be slow.
Digression over - what's this got to do with the Amazon, Google or Microsoft cloud?
When you rent a virtual server you need to know that the physical hardware is going to be up to the job and not over-committed running too many virtual servers. A client has just sent this link over http://www.infoworld.com/article/2610403/cloud-computing/ultimate-cloud-speed-tests--amazon-vs--google-vs--windows-azure.html which demonstrates that Google's cloud servers are not only faster than Amazon's or Microsoft's but actually cheaper too.
If you need advice about switching your Alpha Tracker or other system to the cloud, do get in touch. In this fast-moving area it isn't easy to keep up and sometimes some plain-English advice can really help.