Quantum mechanics in drug design

We've seen that quantum mechanics produces some weird effects, namely...

• Energy comes in discrete lumps (instead of being smooth).
• Position is governed by probability (instead of being well-defined).

In a 2007 Drug Discovery Today article, Raha et al discuss how these properties are vital in drug design. Read over their article and post in the comments below an answer to the question: What is one example of how they use the weirdness of quantum mechanics (discrete energy and/or probabilistic position) in drug design?