I (still) use a Nexus S phone. I am using Cyanogenmod on it. After an article in a computer magazine I decided to give the ART-runtime a try instead of the default Dalvic-runtime. Unfortunately I do not have enough free space free (and all what I can is moved to the USB storage already) to really use the ART-runtime.
After switching back to the Dalvic-runtime, I had only 2⁄3 of the previously available space free. After a little bit of looking around I found /data/dalvik-cache. I deleted with a file manager the content of the directory (you will get some “app crashed/died” messages) and rebooted the phone (this is not the same as formatting the cache partition in the recovery system).
During boot it populated the directory again and now I have more than 4⁄3 of free space on the internal storage.