If we judge Java by Eclipse, can we judge C by iTunes? :-) They both tend to become unresponsive at odd times, but it's caused by clumsy background processing, not language performance.
The Eclipse framework itself is plenty fast, and UIs based on Eclipse RCP can be quite snappy. (Except for that damned startup time.) Swing's a mess, but if you're looking for the technical limitations of a language platform, it's the best performers that are relevant, not the worst performers. Otherwise, iTunes is evidence that even C is just too slow.
The Eclipse framework itself is plenty fast, and UIs based on Eclipse RCP can be quite snappy. (Except for that damned startup time.) Swing's a mess, but if you're looking for the technical limitations of a language platform, it's the best performers that are relevant, not the worst performers. Otherwise, iTunes is evidence that even C is just too slow.