Basically, it's an APK you push to /system/app and when you run it, it...
- Reboots your device
- Odexes everything in /system/app
- Deletes the dalvik cache and it's own APK (as you only need to run it once)
- Reboots the device and rebuilds the dalvik-cache
Of course, odexed /system/data means you can't make any /system/framework changes, but how often do you need to do that? If you DO need to, you can reflash your ROM, do the changes, then run OdexMe again.
As I say, this is written for and tested on MCR, so if you try it, backup first and use at your own risk.
You can check it's worked by looking at /system/app after reboot, it should have a bunch of odex files, plus /data/dalvik-cache will have shrunk lots.
You can grab it in this post and one last thing - the initial reboot and odex takes a while, so be patient.
ROM devs - feel free to include this if you like it in your ROMs, but please let me know (and give me credit) so I can contact you when a new update comes out (i'm working on the next release with a few other tweaks).