Google Spreadsheets is the newest application to use a GData API -- a library that allows programs to use Google products outside of the Google environment. Philipp explains that you cannot use the API to create or delete spreadsheets yet, but you can do pretty much anything else you would want.
"According to Google, with the Google Spreadsheets Data API you’ll be able to:
- view spreadsheets
- edit/ delete content in spreadsheets
- request a list of existing spreadsheets
- query a spreadsheet’s content
You can’t however (at this time) create new spreadsheets, or completely remove existing ones." -- Philipp Lenssen
You can view an example application using this API here.