Google announced today that in the first 24 hours of availability, Gmail users placed over 1 million calls . That's very impressive considering many accounts still do not have access to the feature, which is being rolled out gradually. The new VoIP service allows US users to make calls to any number in the US or Canada. International rates are low as well. It just goes to show you what can happen if you integrate a new feature into Gmail.
This early success indicates that users are prepared to make real use of VoIP services. When Google added Buzz to Gmail, many decried the pollution of their sacred Gmail interface with all the Buzz information. If you get the notice that the Gmail call feature has been turned on for your account, you might as well try it. Everyone else is.