In case you haven't seen the announcement on the OpenSocial blog, some changes to the way iGoogle's REST and RPC endpoints verify requests will be going live today, on the developer sandbox. If you're using a client library (Java, PHP, Python, Ruby), the latest versions will be compatible with these changes.
To ask questions about the client library changes, please check out the client libraries group. As always, for other questions, see the iGoogle developer forum.