It's been long since version 0.9f and a lot of improvements and fixes have accumulated, so it's quite a good time for a new release. As already mentioned in the newsgroups, this release is significantly faster due to optimizations in the SUBTYPEP routine, plus some minor fixes in the compiler.
As side news worth mentioning, SLIME has been ported to ECL and work is going on slowly but steadily on making the compiler more stable and efficient.
Finally, ECL now finally compiles with GCC 4.0 on Mac OSX. It seems that there were some problems with the evaluation order of some C statements -- you know, one gets used to the lisp rule that things are evaluated from left to right, but in the C world the compiler is free to reorder everything, changing the semantics of even the simplest assignments.