It currently works with the following browsers: Chrome v5/6, Firefox v3, Safari v5 for Mac and Internet Explorer v8. The main benefit seems to be speed in accessing results but there haven’t been any claims of a positive impact on accuracy. Saving between two and five seconds per search really wasn’t top of my list of priorities. Having said that, I’m curious to try it out on Google Scholar and am already imagining how predictive search might be realised in library catalogues.
You do have the option to turn the feature off from your preferences, though Google Instant is only currently available from the Google.com domain and if you are signed into a Google Account. Personally, I tend to use my browser’s search box rather than navigating to the search page anyway so the impact on my search habits won’t be much.
The mobile version is expected soon, which is an environment where speed can have a big impact and I’m curious as to hear more about the reasoning behind this development and where it will go from here. As a first impression though, it made me wish Google adopted more of the mantra, if it ain’t broke..