Yahoo has jumped on the Video Chat bandwagon. I haven't tried it but it sounds from this article like it's cross platform and no login required. And, it's Flash based (boo hoo iPad 2) so should work on the PB.
Works on my desktop but when I click on the link (that I sent myself) on the PlayBook, I just get a screen with the spinning wheel where it says it's checking my camera and microphone. Maybe Flash 10.3 will help when it drops.
I wasn't able to try this at work because they block video. Just got home and tried it and had the same result as everyone else. Tried it on my desktop machine and got a popup saying that Flash 10.3 IS required. Looks like once we get the 10.3 upgrade that this might be an acceptable cross-platform solution. I've tried Reel Portal but found it kind of crude looking with poor quality video and you have to use headsets due to terrible feedback in the audio.