A good IDE, with good autocompletion features increases productivity a lot, plus it makes much easier for begginners to get started.

When you first starting, you don't know much of the API/features of a language, hence IDE features such as "Autocompletion", "Open Declaration", "Find References"... are extremely useful.

One of my frustration with working with Python is that none of the IDEs are that good, and methods/language features are not commented that well.

In the Java world, Eclipse + lots of code commenting = makes it insanely easy to get learn new APIs. Also, IDE's help a lot with debuging, running external tools, some automation...etc.

IDEs usually have higher learning curve (vs. a normal text editor), but make it up with the features that they provide.