IDEs for dynamic languages - how far can you get?

Question

I find it frustrating how the speed of development that dynamic languages should offer gets significantly compromised by the lack of completions and other assets that IDEs would give you in their static counterparts.

It's not just about typing less - it's the productivity boost and plain fun you get by browsing APIs without constantly having to refer to a documentation that is not integrated with the editor.

To date all IDE + dynamic language combinations -which to be fair aren't that much- I've tried were:

• buggy
• slow
• clueless/overenthusiastic (as in showing all completions ever possible)
• or simply not as complete as, say, Eclipse + Java.

I'm aware that dynamic code analysis is not a trivial task. But one can't help wondering - is this piece of code really so hard to figure out?

So my question is:

Have any particular IDEs (or less all-in-one setups) achieved a totally outstanding support for a dynamic language, or is this still an 'unsolved' problem?