Rick, a member on on the C# team responded in the feedback section of another post. It was interesting enough that I thought i'd bring it up as a post. He wrote:
I'm a usability engineer that's been working on Visual Studio for the six years, so I've seen hundreds of people using Intellisense in the lab and their offices. As a result I have strong opinions about the feature. One thing that I always remind people to keep in mind is that people use intellisense for two things:
One interesting thing to watch is how people switch quickly from one to other, often every few seconds when they are really in the zone. Any changes that impede one of these uses at the expense of the other is going to be very frustrating.
Take, for example, the idea of filtering the list down to match substrings. This would work well for times when you are pretty sure you know what you are going to type. However, if you realize that what you thought you were going to type isn't actually in the list, you can't just use the arrow keys to scroll down through the list, you have to delete what you already typed to let the list expand back. At this point you are now thinking about how to use your tool instead of your program, and you get frustrated.
As people on the C# team know, I am very skittish about altering Intellisense because it seems easy to do more harm then good, especially when the feature works so well so much of the time due to it's simplicity and predictability.