Bitcoin have an potential to overtake dollar in future, but at a moment it seems that people will only use bitcoin, as many of people are not aware about bitcoin and people who are comfortable with dollar will continue to use it.
No overtaking is not the right term. If bitcoin will overtake dollar we won't see some nice profit during exchanges. Maybe the best term would be powerful currency over all.
Actually if it is the price we are talking bitcoin got a larger price now and is being numbered though dollars. But that doesnt say how powerful a currency is. Chaser is right if bitcoin overtake dollar we will get some really bad problems.