Of the four billion prescriptions written for drugs, only 25 million were submitted electronically according to this article at Pharmalot. This could be changing in the future, as the two big companies in the prescription drug world are calculating a merger. The two networks are composed of Benefits Managers (such as Medco, CVS Caremark, and Express Scripts) and drug store chains (such as Walgreens, RiteAide and Walmart).
According to the article, health insurers, business groups and the federal government have been pushing physicians to prescribe medications electronically because it eliminate some of the mistakes made and save lives of those filling the prescriptions. The temporary name for this entity is SureScripts-RxHub and there will be 200 million Americans who benefit from this new merger, as 70% of US pharmacies will have the ability to accept electronic prescriptions.