Thanks to MOW for a pointer to A Hey Scripting Guy blog entry by super-star Bruce Payette. This article comes from part of his recently updated PowerShell In Action (2nd Edition).
In windows, events tend to happen asynchronously – rather than synchronously. An event typically occurs in some other process or some other part of WIndows aside from the PowerShell console you are using to handle the event. This takes a different approach to writing PowerShell code as Bruce explains.
This section of his book should convince you to buy the book (unless like me you already own it). Go and buy it. And to save 35% use Promotional Code payette22035 when you check out at www.manning.com.