Google's at work to make it possible

http://googleblog.blogspot.com/2007/01/real-time-quotes-for-free.html

[Moved from "realtime quotes in Google finance" – Tony]

quote from official google blog:
Today, the NYSE has moved the issue a great step forward with a proposal to the SEC which if approved, would allow you to see real-time, last-sale prices across all Google properties including Google Finance, Personalized Google, Mobile, and of course, Google.com. It won't matter if you're on Wall Street or Main Street – you'll have free, easy and fast access to real-time prices from NYSE on Google.
http://googleblog.blogspot.com/2007/01/real-time-quotes-for-free.html