As a rule, some things are not going to sound cool. The advertising industry faces this problem on a regular basis. How do you make toilet paper cool? How do you make people care enough about which toilet paper they're going to use?
Luckily, a new Jewish social network has solved this problem. If you use a the word 'Kool' in the name of your site.
Honestly - I thought mis-spelling cool fell out of trendiness in the eighties.
Also, social networking should be about connecting with your own friends, and then gradually expanding it out. Limiting yourself to a particular group of people is rather closed minded, and indicates that you're only able to make friends with people who are extremely similar to yourself.
This isn't the only religous one, someone's setup MyChurch.org and also muslimspace.com.
The problem with social networking sites is that they are very cheap to setup the technology, the difficulty is in getting people to use them. Leveraging existing communities looks like a good idea. However, it has to be done very well.
Myspace succeeded by lassooing the trendy kids - music + teenagers + customisation. Facebook managed it by being exclusive and playing up to kids who'd just joined university. Piczo grew around the idea of sharing photos. Not sure what Bebo did, but I'm sure it didn't grow by associating itself with religon.
Religon is all very well and good for attracting people of a certain age. The question that has to be asked: is religon really an effective marketing tool for people under 25? I think the lack of 'Jesus Cola' shows that it is. In fact, the only religous brand I can think of is 'Quaker,' which I think has slowly died since Nestle bought them about ten years ago.
PS. I'm sure Jesus Cola actually exists, but it's definitely not of a size to register against the Cola giants.