While it's impossible to determine the exact number due to the number of factors involved, we can get a fair estimate. Let's take a look at the numbers.
The Department of State received over 9.1 million qualified entries during the 60-day application period for DV-2009. (Note: the 9.1 million is the number of qualified applicants. It does not account for the number of applications that were rejected because of ineligibility.) Of those 9.1 million qualified applications, approximately 99,600 were registered and notified to make an application for one of the 50,000 available diversity immigrant visas.
That means that for DV-2009, approximately 1% of all qualified applicants received notification to make an application and about half of those actually received a diversity visa.
All qualified applicants have an equal chance of making it through the random selection, so be sure that you meet the eligibility requirements and submit a complete and correct application. It is also recommended that you apply early on in the registration period to avoid the system slowdowns that sometimes occur at the end of the registration period.