http://www.mameworld.info/ubbthreads/showflat.php?Number=308967
One of the most interesting features added is the lua scripting support. There are some really cool things that can be done using lua scripting such as being able to display your CP, instructions, move commands etc. over MAME without the need to compile a custom version. It does say it's a "basic hookup" at this point so probably not much that can be done yet but it will be interesting to see where they take it.