not alone
I've had these problems for about a week now. And on 2 different Macs running different versions of the OS (10.2.8 and 10.3.4), using different webcams, and accessing the internet with different ISPs.
The problem suddenly appeared one morning - no cam - and not being able to view a friend's cam.
The problem I had was as follows: on the mac running 10.3.4 YM would crash when I tried to start the webcam. On the one running 10.2.8 it would show "connecting" then, immediately, "stopped". On both, a friend's invite would give the response "This user doesn't not have his/her cam online".
On the mac running 10.3.4 I fixed permissions, and suddenly I got my outgoing video picture back, without it crashing. Curiously, without doing the same on the other mac, my video was back. None of this really mattered, as no friend could view my webcam and I still couldn't see others.
I've trashed permissions to no avail. I've reset the firewall with proxy settings and opened a specific port for YM to no avail. I removed YM and reinstalled to no avail.
I've contacted Yahoo twice. the only response I had is that the feedback I've given might help their engineers who are working on it. What "it" is is unclear.
Sorry for the ramble. Nothing to help, just my experience.