Point guard is arguably the toughest position to gauge future pro potential. Running a NBA team takes a lot of skills that are often hard (or impossible) to assess in college prospects. Because of the unique and hard to define demands of the position, many future All-Star NBA point guards have dropped in the draft over the years.
That said, when a point guard is selected very early in a draft, he usually turns into an excellent pro. It is an auspicious sign if a point guard prospect is regarded highly enough to be picked in the top 5, and especially promising if he is selected in the top 3. Let's look at all the point guards chosen in the top 5 since 1990; the players in bold were an All-Star at least once:
Allen Iverson, Derrick Rose, John Wall, Kyrie Irving
Gary Payton, Kenny Anderson, Jason Kidd, Mike Bibby, Steve Francis, Jay Williams
Mahmoud Abdul-Rauf, Anfernee Hardaway, Chauncey Billups, Baron Davis, Deron Williams
Stephon Marbury, Antonio Daniels, Shaun Livingston, Chris Paul, Mike Conley, Russell Westbrook
Devin Harris, Ray Felton, Ricky Rubio
That's a very impressive list, with a high success rate and few busts. Of the 24 point guards drafted in the top 5 since 1990, 15 have been All-Stars. And 11 of the 15 taken in the top 3 have been All-Stars.
Basically any point guard prospect drafted in the top 3 we should expect to turn into an excellent pro, barring injury. Most drafted since 1990 have become All-Stars, and even those who didn't have been good. Bibby was a borderline All-Star talent, and Wall is moving in that direction. Jay Williams had a decent rookie year, but then was injured and never played again. Mahmoud Abdul-Rauf wasn't a star, but was a good NBA player nonetheless.
So the top 3 is a special place for point guard prospects. Picks four and five have obviously been very fruitful as well. Overall there are probably fewer busts among point guards selected in the top 5 than any other position. Point guards aren't picked in the top 5 every year, but when they are they usually turn out being worthy selections.
In terms of the 2013 Draft, this information is probably only relevant in regards to Marcus Smart (unless Trey Burke or Michael Carter-Williams really catch fire over the next few weeks.) If Smart is drafted early and can stay healthy, history says that he is almost guaranteed to become a very good NBA player.