I moved from emacs to eclipse, for python development, 3 years ago. Why? The nicely integrated subversion integration (subclipse), the SQLExplorer plugin, and PyDev. I only really use the editing features of pydev, I hardly ever go into debugging mode. I code everything these days using TDD and have eclipse set up to run nose (the test discovery script) on whatever is selected, be it a file or a directory. It also gives me code coverage.
I still love emacs but the future IMO is with eclipse.
I use eclipse when I need the debugger, and for certain code editing tasks (it understands Java code in a way that emacs doesn't... though I'm sure someone could write elisp to solve it) and emacs when I want to impress my friends.
The way I view eclipse is that in general its pretty awesome when the plugin you're using is well developed and thought out. When the UI is nice, everything works great. When you're in mushier territory, emacs (and vi) are like text-editing power saws, they're pretty good at moving text around, but rarely understand the code, so the things you're used to working are pretty much always available.
Which direction do you see things going? I personally feel that more effort is being put into eclipse, hence it has a longer term future.
A big win for Eclipse is the ubiquity of an easily installed, strong, consistent virtual machine across OSes. Cygwin is a great achievement but too much like hard work. I'm compelled to use Windows in my day job, with no admin access, and being able to use the same development environment with my linux box at home is great.
If you do anything in Java, people will ask for Eclipse integration. Clearly the market has spoken in Java-world ;)
Emacs is good because people who are "good at Emacs" are good at text-editing in general. The tool is more general, but that means they can maintain the majority of their output speed in a new language, or a language where things like automated refactoring are tricky or impossible to reliably do (say, Ruby)
BTW: I'd say "easily installed, strong, consistent" applies more to text editors than IDEs. Emacs has a windows binary thats pretty reasonably sized, whereas Eclipse is in the hundred megabyte range and Visual Studio (insert chuckle here).
I still love emacs but the future IMO is with eclipse.