I was already an Eclipse user, as I develop in Java. However, when I heard about Abap in Eclipse (as developed by SAP; maybe they're confusing it with some earlier non-SAP attempts), I was not really terribly enthusiastic. The reasons were that I was happy with the editor in SE80 - we have predictive text, we can drag and drop from the object tree to an extent. So I couldn't see the point.
Then I had some hands on.
I'd forgotten what a modern IDE brings. It's not just prediction, it's refactoring (although there is more of this in later "se80" development environments", it's organisation and it's syntax checking on the go - including warnings. All these lead to more chance of spotting errors during development - which is when it is cheapest to fix them. The whole environment is geared to make this easy.
Ok, now, what about those who really just don't want to shift. No problem. Implement Eclipse, and show them how they can have SAPGui and therefore SE80 in an Eclipse window. Soon or later, they'll start playing and get hooked in...
Therefore, there is no reason not to use Eclipse, and every reason to get your mitts on it as soon as technically feasible!