We've been testing it at work today.
I like the fact that the application doesn't need to be open or running in order for you to recieve a call.
It seems pretty quick, voice and image quality obviously dependent on your webcam quality etc (I was testing on an iPhone 4 and MacBook).
It crashed on me once, which locked up the entire OS. I could move the mouse, but nothin worked, a restart fixed it.
I tried calling my collegues MacBook Pro upstairs, by adding his email address to the address book, and calling that. It worked perfectly.
I would love for you to be able to leave messages -that'd be just awesome. The option to invite other callers (in some way?) would be great too.
Overall for a beta it works really nice, search is an obvious function i would like in the future though, im pretty confident they would have that.
Thank god it doesnt auto accept calls too, that could be embaressing
I would also like the ability to assign caller pictures for when they call you/you call them.
If anyone wants any info about it, ive got it running here.