Web Video Conferencing

Two of my startup development clients have recently discussed adding video conferencing to their web offering. Both startups use have two kinds of users involved who are going to want to do 1-to-1 communication through a variety of different communication approaches (text, phone, etc.) and now they want to explore providing video chat between the parties.

An equivalent example (drawing from my eHarmony days) would be providing video chat in a dating site. Since you don't know what users of the site have installed and you would prefer that there's not a lot of downloading required. In looking out there, it seems like there are some flash-based solutions like Sightspeed, ooVoo, SnapYap and Tokbox. Skype would seem to be out because of the fat client download. I even would think that someone having to do a download like WebEx does would be annoying enough that users wouldn't want it.

On the flip side, I would want the system to "call" the person to see if they are available to receive the video chat and/or show them as "not available" if they can't receive a video chat at that time.

So, how could I provide easy-to-use video chat to the users of a dating site?

I'm likely going to need an API to set up various "channels" that will allow on the fly chat sessions or to associate sessions with manually created channels.

Being start-ups and given that we don't know the usage levels, we'd like to keep things cheap.

So, some questions I'm hoping to figure out shortly:

1. Are there examples out there of sites who are already doing this for their users? I'm not asking specifically about dating, but rather having integrated video chat.
   
2. Am I missing video services that would work?
3. Do I need an API for integration or are there other ways this could work out?
4. Is there a good way to make this as nice a user experience as possible?
5. Finally, any thoughts around the viability of video chat for something like a professional networking site? Make sense or not? Are we too early still for the technology?
   

Any thoughts or help would be greatly appreciated.