Although it is still a beta, Google Talk is a promising service. And if look into the fact that some of its new features have not been announced yet, we can say that Google Talk is going to became one of your favorite messengers. One might find it very simplistic and not so impressive as the yahoo messenger or the MSN, but if you want a messenger that can do the job well and effectively, with no unnecessary visual effects, this is the messenger for you.
And don't forget, it is still a beta. A lot of things are to be changed in its final version and of course a lot of new features are due to be added.