Most notably it adds lots of additional SSD teaks and functionality and (At last) support for reading smart attributes in Storage Manager.
Release Notes:
http://download.adaptec.com/pdfs/readme/Relnotes_ARC_FW-b17899_ASM-18570.pdf
Release Notes:
http://download.adaptec.com/pdfs/readme/Relnotes_ARC_FW-b17899_ASM-18570.pdf