I'm one of the people who find it difficult to change their own habits. For example, three years ago I had to change the email client I used at work. Although there were not many conceptual differences between the two tools, I didn't feel comfortable using the new one and I failed badly to keep my emails organized. What a mess it was!
Only after one of my colleagues had given me a hand and showed me how to use the tool effectively, I picked up the tool's philosophy and became fluent with it.
Switching an IDE is far more challenging, because IDEs are very complex and the level of comfort and confidence in the tool that developer have to feel is much higher than for an email client. A good IDE becomes effectively a direct extension of the developer's brain and even small incompatibilities are immediately reflected in decreased productivity and enjoyment.
I hear some people have troubles evaluating IntelliJ IDEA and learning to use all its powerful capabilities. It's understandable given the effort required to properly understand the philosophy and usage patterns of a modern IDE. And here comes the good news:
If you are an Eclipse user and think of giving IntelliJ IDEA a good test ride, I recommend you tried the IntelliJ IDEA Evaluation Guide for Eclipse Users. It will assist you during your evaluation process, tell you about the similarities and differences of the two IDEs, help you customize key shortcuts, open your existing Eclipse projects in IntelliJ IDEA and a lot more.
On top of that, you might also find useful the flash demos on using IntelliJ IDEA, which show a lot of the principles in action.