"Java is slow, interpreted language." This statement was true at least in the very first years (or months) of Java. Since JDK 1.3/1.4 the peformance is getting better and better. The newest JVMs becomes even more efficient, than C. The c-compiler is static, so once compiled code cannot be optimized any more. The HotSpot is able to perform optimization on the fly, but the optimizations are based on statistics, which are not available at compile-time. Now the conclusion: because HotSpot is written in C itself, it cannot be so fast as Java :-). Beyond that C is not very good to maintain. This is basically the idea of the research project maxwell (actually a cool name). James Gosling mentioned this project during the informal interview at the Sun Tech Days in Frankfurt, and said something like: "it begins to turnaround". It's really an interesting idea - a short (21 pages) description is available as well.
NEW MUC Airport Workshop: Migrating Java Client (Swing / Java FX) to Web Standards