Along with battery life, sudden power cycles and simultaneous appearance of 3G and WiFi icons a serious security issue is also fixed in 2.3.4 release.
The ClientLogin authentication protocol implementation was not proper in version 2.3.3 and earlier. After a user submits valid credentials for Google Calendar, Contacts and possibly other accounts, the programming interface retrieves an authentication token that is sent in cleartext. Because the authToken can be used for up to 14 days in any subsequent requests on the service, attackers can exploit them to gain unauthorized access to accounts. I never expected such moronic mistake from google. Nevertheless I am on 2.3.4... :D