People who were exposed to the VIM editor at a young age tend to become addicted to its keybindings. I recently discovered the Vrapper Eclipse plugin that although still young and not as featureful as some of the plugins for other IDEs listed here made using Eclipse a much more pleasurable experience.
The usual reason a heavy VIM user would consider using Eclipse is for its Java refactoring or C/C++ code browsing, "find all call sites of function F" features. The C++ parsing and code completion part in particular is something proprietary tools like Source Insight does a lot better then older open source tools like cscope.
In a previous job, I hacked extensively on a code base where Java code with deep class hierarchies and C and C++ code from different vintage and style was linked into a single Linux process. Some of that code implemented device drivers in userspace using a chip vendor supplied abstraction layer which is of course not as well designed as the Linux kernel driver API. I relied on Eclipse and cscope + VIM to navigate the Java and C/C++ part of that code base respectively. I wish I could have used the Vrapper plugin then.