Josh is using the M555b: http://www.theverge.com/2012/2/24/2821762/whats-in-your-bag-joshua-topolsky"So I smashed my Logitech M555b while at Microsoft research, and then picked up an Arc Touch mouse because I thought it would travel better and be more comfortable. Wrong. Not only is it uncomfortable to use, but it has a wireless dongle! I grabbed this M525 in the short term because I couldn't find the model I had, but I have since secured a new M555b. Phew."