This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Java 7 has added additional capabilities such as in the NIO.2 features that were not available in earlier versions. If your application needs these features, then you need to use Java 7. For example, Java 7 supports the join/fork framework. While it was possible to perform a similar type operation in earlier versions, it is much easier using the new framework.