The spreadsheet in Google Docs now supports independent form entry. That means that if someone wants to use a Google spreadsheet as a database, they can ask others to fill in data by putting information into a nice, compact form, instead of into the spreadsheet itself.
As is typical in Google Docs, this feature is simple, easy to use, but somewhat underpowered. For example, the form cannot be easily embedded in a Web page, and there's no data validation on form entries. I still recommend WuFoo for online data collection, and there are other good online databases allow embed forms (and export data to a spreadsheet for quick processing).
A pretty sweet feature is that users can easily e-mail the Google form, if all they want to do is collect a bit of data from people they know. Also, if the spreadsheet is open on a computer, the data coming in via the form can be monitored in real-time, which is, frankly, bad-ass. Try entering data in a form here.
I do expect this feature to evolve over time. Because of this evolution, I do not give good odds to the long-term survival of the other online databases. In fact, I fully expect Google to release a database application into Google Docs to go along with this bare-bones data-entry function.