It's funny because I had a really refreshing experience with Pharo lately. A part of the workspace threw an exception and I was presented with the option to debug it. Hitting debug brings up a debugger with the full stack available and the source of the error. Within a few minutes I was able to track down the error, fix it and have the fix go live immediately. Compare this to what it would take to debug and fix an error in, say, Eclipse. The difficulty of checking out the Eclipse source, dealing with potentially confusing and convoluted source code, wrangling with a labyrinthine ant or Maven build process etc. makes it not worth your while to fix the problem.
Whatever the pros and cons of the image based system may be the immediacy and transparency of it is really enjoyable. It's a shame that the idea has been pretty much abandoned by all but a small contingent of developers.