The truth is that, at least initially, you don't really know the person that you are talking to online. All they are to you is a series of words and possibly a photograph, and with that sort of ambiguity it can be easy to create any number of different impressions or images. Detractors of online dating will always point to the extreme examples of physical meetings gone awry after online courtships. I would argue that these examples are extreme and actually more infrequent than with similar stories involving traditional dating. However, they do illustrate several basic guidelines that should be adhered to when you begin to date online.
First and foremost, never proceed at a pace that makes you feel uncomfortable. Whereas in a physical setting you can generally get a "read" or a "vibe" as to the sort of person you are speaking with, online dating makes that sort of gut impression more difficult to come by. It can take extended conversations before you feel comfortable enough to actually meet somebody, and that is perfectly acceptable. Remember that you truthfully don't know this person at all, and if they begin to pressure you into meeting them sooner than you're comfortable with, it may be a good idea to simply nip the relationship in the bud.