In the past, when I've used services like Skype and Gizmo (which was acquired by Google last year), I've been very happy with the experience and with the added features these services can provide (such as easy call recording). But I've never been a particularly heavy or regular user of these services, sometimes going months or even years between using them.
This has led to the problem of constantly forgetting details about my account, such as my username and password, or even the email account I used to sign up for the calling service. Which can be a big pain as usually, when I do need to use them, it is right away and I don't have much time to dig around and find the info I need in order to log-in (and often I also need to upgrade or re-install the software).
But the new Google service solves all of this simply by being part of Gmail, which I do use on a daily basis. So any time I need to use the new Gmail phone calling features, I don't need to worry about forgetting the login info as it is already part of Gmail.
As far as the service itself goes, it is pretty bare-bones but still effective. Once the browser-based add-on is added to your browser, a small phone icon appears inside the chat area of the Gmail interface. Clicking this phone icon brings up a dialer that can be used to call any phone.
Quality has proven to be good in my tests and one very cool feature makes it possible to transfer an in-session call to another phone. So for example, if you start a call in Gmail on your computer and need to leave the desk, you can transfer the call to your cell phone.
Of course, you need to do this as there is currently no mobile version of this service (which does work on Windows, Macs and Linux systems). Also, in its base version it is not possible to receive calls, though users only need to upgrade to the free Google Voice service to get this capability.
But so far, I'm pretty happy with this new feature of Gmail.