The chances of it working out are half half. Firstly, if the site can be trusted and it depends on what kind of people are using it. I think that online and real life is not that much different. I mean, relationshps that are face to face don't work out as well right? Online can work out and it can't as well, it's just like real life. Be careful though, don't try anything too risky.
Of course they do. It's just they have less of a chance of working out because your not near them most of the time. And in order for them to work out it takes twice as much work and maturity.
I've never tried it myself but have a friend who has met three different guys online. The relationship was great as long as it was online, but as soon as they decided to meet things went bad real fast.
Online dating sites: rarely
Online community sites: such as forums, facebook, message boards etc, meeting on these is better, cause people are less inclined about dating, and have a lower defense.