Yup it's a nice service but I never used the arrival one though...I usually just shower at the hotel

By the way, it is also available to JMB Diamond and JMB Sapphire. Here is the page (in Japanese)
http://www.jal.co.jp/narita-t2/campaign/shower/ (looks like GGD03707 has edited his post and included the same link...oh well )