In the blog post Why I Think IDEA Going Open Source is Not a Good Sign, Cedric Otaku articulates why he believes that the open sourcing of IntelliJ IDEA Community Edition is not a good sign for that IDE's future. He makes several points that are very difficult to argue with and many of which I thought myself.
There are three stated reasons in the IntelliJ IDEA Community Edition FAQ for providing an open source Community Edition of the IDE and the platform upon which it is built. The first stated reason is to "significantly grow the number of users of IntelliJ IDEA." I have no doubt that this will be the case, especially in the short-term. The second stated reason is to encourage the "growth of ecosystem around IntelliJ IDEA." The final stated reason is to improve both the open source Community Edition and the premium Ultimate Edition via expected increase in user feedback.
Ceki Gülcü has written a response to Otaku's blog post called IDEA open sourced and points out that this may be a "strategic decision" that turns out okay for JetBeans in the end. However, Gülcü also concedes that Otaku is probably correct that "Jetbrains is unlikely to be flooded with patches and additions from the community."
In Hybridizing Java, Bruce Eckel pointed out that "Cost was one of the main things that originally held me back from using Flex, primarily because of readers who were unwilling or unable to pay it." When Adobe made large chunks of Flex 2 SDK and compiler freely available and later open sourced Flex 3, they opened the doors for Eckel and numerous others to adopt Flex. The Flex user base has grown tremendously since then. There have been more users contributing bug reports, more third-party frameworks and libraries for Flex development, more books on Flex, and so forth.
One indicator of popularity of a particular product is the number of books covering the topic. A simple search on Amazon.com for "Eclipse IDE" (IDE portion is important to avoid the Twilight book getting in the way) returns numerous books on Eclipse including, but not limited to, Eclipse, Eclipse Cookbook, Eclipse for Dummies, Professional Eclipse 3 for Java Developers, and Eclipse: Step-by-Step. Additional Eclipse books are listed in Eclipse Resources.
Amazon shows many books on NetBeans as well: NetBeans: The Definitive Guide, The Definitive Guide to NetBeans Platform, Pro NetBeans IDE 6 Rich Client Platform Edition, 100 NetBeans IDE Tips and Tricks, and many more. Additional NetBeans books can be found on the Netbeans Books page.
If you want to see a ton of books on the same IDE, try placing "JDeveloper" in the Amazon.com search. A listing of a small sample of these books is available at JDeveloper Books and Courses.
There are numerous books on Eclipse, NetBeans, and JDeveloper. For IntelliJ IDEA, however, an Amazon.com search only lists one book devoted to the topic: IntelliJ IDEA in Action. The Community Edition FAQ states that this book covers IntelliJ IDEA 4 and IntelliJ IDEA 5 (IDEA 9 will have the Community Edition), but adds that there are negotiations underway for a new book. Technical books are not known for being financially lucrative in general, but it does help encourage a publisher to publish a book on a certain technical subject when it is anticipated that there will be high demand. Perhaps open sourcing the Community Edition of IntelliJ IDEA will help stimulate this demand.
Intellij IDEA has an almost cult-like following of die hard enthusiasts and that speaks well of it as a product. This recent announcement of a Community Edition of the product may be just what is needed to increase the number of loyal users. In some cases, developers new to the IDE may even decide they want to pay the license fee to move to the Ultimate Edition for use with the Enterprise Java needs, Flex development needs, or other needs above and beyond what the Community Edition provides.
Of course, IntelliJ IDEA's future is not in a vacuum. As I wrote in a recent blog post, the Java IDE market has other forces at work. Another major external force is what Oracle decides to do with NetBeans once its (Oracle's) deal with Sun concludes.
I can only speak for myself, but I can say that it is likely (at least it's in my current plans) that I will start using IntelliJ IDEA Community Edition in much of my Groovy development. I will be likely to blog on things I learn as I do this and possibly use screen snapshots of IntelliJ IDEA with Groovy code and support. This is just one small example of how exposure for IntelliJ IDEA might be increased as a result of the move to an open source Community Edition. The question of if additional users and more coverage will translate to more revenues can only be answered in the future.