I started using Eclipse as my first Java IDE back in 2004.
I had always written code in Java, since version 1, but back in those days I was using some very simple editing (even the Microsoft Edit, it was even before I started using Emacs!) or some less expensive (in term of resources) IDEs.
My switch to a "real" IDE was during the fourth year of University, when I started using Borland. I remember the IDE was around 80 MB in size and required almost a minute to start on my Pentium IV. Nevertheless it was simple and to the point: it allowed me to develop in Java having syntax highlight, Javadoc inspection, project management and some other feature.
Ok, I have to say it was much more than I needed, since I was working on one or two projects at the same time back in those days. Morever, I was totally unaware of code versioning, and in fact I had developed my own way of doing incremental backups, but that's another story.
While approaching my master thesis, that of course had to be based on Java (not because of choice of mine), I started evaluating some other Java IDE. At that time the Forte For Java was a really famous piece of code, but it was a little hungry on resources and required almost two minutes to start up on my Celeron 700 MHz with 192 MB of RAM. Moreover, while the start up time was not such a big deal for me, having to work for a lot of hours without turning off the computer, the program itself was pretty much unusable with menus half-empty, rendering delays and freezes.
I tried then the Emacs extension for Java, but at that time I was a young Emacs users and the whole JDEE was too much complex for either my fingers and brain.
Having spent a couple of weeks searching for a product, I switched back to the Borland Java IDE, something I already know quite well and that allowed me to be productive from day one.
In the following years I experimented a lot with other two emerging products: IBM Eclipse and Netbeans IDE. However I was not working as a Java developer, or better, Java was not my main language after the university, and therefore I did not spent a lot of time using them for real projects.
In 2004 there was a shift: at the Principle and Practice of Programming Java (PPPJ) conference in Kilkenny I met Vivek Sarkar, an IBM fellow that shown us the magic power of Eclipse (and of Jikes RVM for what it matters). At that time there was Eclipse 2 (if my memory serves me well 2.2) and the main feature that astonished us was the "refactoring" capabilities of Eclipse.
Once I was back home I installed Eclipse and switched definitely to such environment, letting Emacs for quick-and-dirt editing.
Several year later, at the time of version 3, I got back to a Java-based job and developed an application with the Rich Client Platform (RCP), so I used Eclipse to develop another Eclipse application (a kind of recursion that computer scientist seems to appreciate very well).
Then I had to manage a PHP codebase, and did it with Eclipse too even if, I have to admit, the support to such language was not mature enough and the editor had some lag.
Today I use Eclipse on a regular day-by-day basis mainly for web development, and mainly for Java because I use Emacs for all the rest.