On Monday Google Docs added two new data APIs to their spreadsheets: Table Feed and Record Feed. What this means is that instead of paying for SQL hosting you can run a database through Google Docs! Of course there are limitations and maybe security concerns but this is a major announcement regardless.
I've already set up a spreadsheet to keep track of downloads for MY STADY. What I did was create a form to collect the necessary info to a spreadsheet. Using the feed API and Yahoo! Pipes the information is formatted to a blog post. I plug the Yahoo! Pipe into Twitterfeed which sends new posts to MY STADY via Ping.FM.
That's a really simple example but the possibilities are limited by your imagination. I bet someone's already working on a Google Docs message board.