I've been using Slim ICS for a few months now, and I thought I'd share some of the tweaks that I have been making to it so that you can all reap the benefits.
I have been messing around with how to maximise usage the "fast" storage on the phone. Right now I am using a heavily rewritten version of the 30datafix script that is floating around on the forums here. It accomplishes basically the same thing, although it links ALL directories and files from /data/data to /datadata EXCEPT /libs and /lib (Gameloft games use libs for some reason). Simply leaving behind the lib folder saves enough space to comfortably install ~150 applications. I haven't noticed any appreciable performance loss for doing so; things still start fast, save fast and close fast. I have attached the script to this post, but please take not that it does NOT remove the symlink located at /data/data OR copy the data from /datadata to the data partition. Hopefully this is something that can be integrated into the ROM from the start so that everyone can reap the benefits.
On a similar note, I have symlinked the /system/lib folder to /data/local/lib. I have saved ~60mb from my /system partition by doing so, and I have not noticed any slow down or stuttering while accessing the SD card (i.e. playing music and using other applications at the same time). If we did this from the start, we could remap the MTD partitions to provide an extra 50mb or so to the /datadata partition at the cost of a ~200mb system partition. I've seen this done before on another ROM, but I don't remember which.
Naturally, if I'm wrong about there being no appreciable performance loss for writing the lib files onto SD instead of NAND feel free to correct me, but at present I feel that this is the best utilisation of my phones's resources.
I hope, and I'm confident, Krarvind will take note of this for the future release.