I just read in some Liferay documentation that IBM's Jikes (java) compiler is faster and more descriptive with compile time errors.
I would like to know whether the community agrees, and whether the switch makes any noticeable improvement in your productivity.
If you are using ants as build system, you can easily switch between Jikes and javac; and then I'd suggest you to try jikes - it's really amazing fast.
Otherwise, you should really consider again because it's not always compatible with your version of JDK and may create extra issue.
Jikes was very compelling in the JDK 1.3 days when the javac compiler was awe-inspiringly slow. In comparison, jikes was blindingly fast. Increasingly, however, the speed improvement is becoming less noticeable, to the point where I personally wouldn't bother any more.
It's worthing noting that the JDK7 compiler has some improvements in the descriptiveness of errors.
Jikes does not support the new Java 5 things, so it is not an option for projects using these facilities.
The best alternative to javac these days is in my opinion the Eclipse compiler which is available in a stand-alone version. Speed (which is jikes primary force) is less an issue these days.
EDIT: Jikes support "incremental compiling" which may be very interesting in environments where development with a full-size IDE is not an option.