I have just been playing with Tafiti, http://www.tafiti.com/. It's very impressive, combining live search and silverlight technology.
For those who don't know, Tafiti means "do research" in Swahili. Even if you didn't know that it probably doesn't matter - what does matter is we need to do all types of research and information mining on a daily basis. By the end of most days I have at least 10 tabs open in IE 7 and quite often am going back to these for reference. I am also using one note 2007 more and more to store random pieces of content. If Tafiti can help on this front to collect and store my findings then its going to be a winner.
Things are moving pretty fast in the race for the browser to become the new OS and I feel this is another step in that direction.
I also started using the spell check in gmail, ok not as impressive as Tafiti, but it is all good for the user experience.