The internet is great for a lot of things and communication is certainly one of them. It can connect you to people you wouldn't normally meet in everyday life and can even filter them down to someone who has the same interests as you. When it comes to dating, this can be a great thing. It can assure that people have things in common and are looking for the same things in life.
However, the internet also allows people to have a great deal of control over how they're perceived. It's relatively easy to paint your online persona as who you would like to be rather than who you are. People can be very different in person than they are online. For example, it's easy to say you have a great sense of humor on a dating site and to write witty things in an e-mail when you have hours to think of them; however this doesn't translate into being funny in real life interactions.
Just as online representations can make someone seem more appealing than they'd be in real life, the way they choose to present themselves online might also lead to them being written off by someone who would be a great match. Just think of all the ways you'd react to someone's profile picture. It's a very heavy first impression. Online dating brings with it the possibility of missing a great person, with whom you might feel an instant "spark" in real life, for a silly reason like a bad profile picture.
This doesn't necessarily mean that online dating is better or worse than traditional dating, but it is certainly different. Also, it seems to work best when it is not used as an alternative to dating in person, but as a supplement. Online dating sites are meant to connect people so they can meet and start a real relationship in person. When two people merely e-mail instead of meeting in person, they develop a relationship with an online persona instead of an actual person.