I've posted full details and a sample on StackOverflow here:
I have some code that uses Invoke-WebRequest to fetch a web page, and then use .ParsedHtml.body.getElementsByTagName to scrape some info from the site.
However, the getElementsByTagName call seems to take a *long* time for me (around 1.5seconds per call) on all three machines I've tested it on (Windows 7 Home Premium, Windows 7 Enterprise, Windows 8). Other people see sub-100 millisecond times running the same code.
There's more discussion about this issue on Google+ here:
I can't find any common pattern between machines that do/don't have this issue. It occurs for me with no PS profile, in both ISE and the console. I have VS 2012 (and therefore .NET 4.5) installed on two of the machines, but not the third.