This is the first time I see this online. You can follow in real time stock quotes!
Try it here:
http://finance.google.com/finance?cid=13756934

Official announcement:
http://googleblog.blogspot.com/2008/06/at-long-last-real-time-stock-quotes-are.html

Google says "Historically, real-time stock data was not freely and widely accessible. Either buried behind subscription walls or brokerage sites, consumers typically had to live with 15 or 20 minute price delays."

Does that mean the new service will make some subscription-only brokerage site really unhappy? And does it mean through screen-scraping of Google Finance, everyone can now add this functionality to their own site as well?

Philipp, probably won't even need to screen scrape. You could use the finance ticker lookup in Spreadsheets to create a feed, or use the Gadget Finance API:
http://code.google.com/apis/gadgets/docs/legacy/finance.html