I don't think IDEs are really a big issue. Having said that, I'm just about done with a first cut at a plugin for IntelliJ (my REPL is being flaky). I understand that Eclipse is much, much more popular, but I like IntelliJ much, much better. Plus, I suspect the intersection of Java developers interested in Arc and Java developers who use IntelliJ will be slightly higher.
A good IDE makes programming easier, but I don't think that Eclipse fits the bill in that regard. I personally prefer NetBeans for a lot of reasons (IntelliJ is much better, and the most recent versions of Visual C#/etc are getting there). I'm not talking about wizards here; there are some things that I like using wizards for, mainly things that are just tedious like creating web service clients for a provided WSDL, I'm talking about useful things like organizing and navigating source code.
A good IDE helps you with large projects, especially with multiple developers, and a bad IDE is just a glorified editor with a lot of extra clutter. Eclipse is that with a lot of extra bugginess, IMO. Given all of the assinine bugs I've found in it, I'm frankly amazed that anyone uses it, let alone uses it as a platform for their own tools (Flex?).
I'm just getting into Lisp again after being introduced to it in college before learning how to program, and I'm liking it quite a bit. I'm using JEdit and DrScheme for the most part, and it's working pretty well so far. But I'd rather use IntelliJ or Visual C# or SharpDevelop, because I'm lazy and don't want to waste time with stuff that isn't actually programming.
I think one reason that Rails has done so well is that the vast majority of the people who use it don't write much code. Most of the code that they "write" is stuff they got from someone else via one of the forums. It's stunningly easy to build a reasonable though generic-looking site in Rails without writing much code, which makes it great for newbies.
For large projects, in my experience Rails falls flat on its face. When I ditched that company, our developers were spending about as much time running unit tests as they were writing code. That ended up being about as agile as a beached trimaster with torn sails. (Rails didn't force us into that approach, nepotism did. A collection of small Rails apps would have worked pretty well.)
