Second life, Pros one a company could have a meeting like IBM did online making it easier for the people who work from home. There is alot of space for advertising.
Negatives, I don't like the idea that you use real money to buy food you don't actually eat or drink. The idea of getting married in second life seems a little wrong if the person is married in real life to some else.
I think it is interesting and scary at the same time. It is interesting in the respect that we have the technology to make this. It is scary to think people will or could become in golfed into this fantasy world instead of going out and leaving their house.