For all of those using VB.NET's Microsoft.VisualBasic namespace specific functionality (or those just interested in the topic) and the performance impact they may incur (if any, and if so, under what conditions) be sure to check out the Visual Basic .NET Internals article on MSDN by Derek Hatchard and Scott Swigart. Much of what they have placed in this article I've been stating for a while in various locations (blogs, forums, and GDN). It's good though to see a lot of this information compiled in one place ;-)
There are also a couple of other links in the Additional Resources section of the article that discuss overall non-language specific .NET performance tips.
I would add the following to the article:
Using CR and LF: the Options
Reading/Writing Structures using FileStream (or just use FileGet/FilePut)
and stress the point that using Option Strict On will significantly improve the overall performance of your application.