XDA forum member Jus10o has managed to get JIT enabled and working on his HTC Hero (CDMA).
Android 2.0 code includes the source code for a Just In Time (JIT) compiler for Dalvik. It detects hot code and then compiles that code as needed providing a performance boost which of course needs to to be balanced against the cost in battery life and memory.
Originally from the Motorola Milestone, JIT works on HTC Sense but is unstable and force closes a lot. However without HTC Sense, and using HelixLauncher by XDA forum member arctu, Jus100 has confirmed that it runs very smooth. He particularly noticed a significant improvement in speed between opening and closing multiple apps.
Currently, the HTC lock screen does not work – the menu button must be used. Other non HTC slide programs appear to be fine. Requires Android 2.0 (Eclair) or higher.
For more information check out the forum thread.