Love it! If you setup on both iPhone and work PC, its a fantastic tool. – Cortana Review

Can be an amazing "virtual assistant" if you set it up to be. My tip: setup on phone and work PC. Connect your emails to it. Cortona will remind you of stuff you promised, to-dos you put in and ones you forgot about. Kind of scary how she reads your emails, but it's been a wonderful time saver and help for work and reminded me about stuff I forgot to do many times!
Review by HelloJAO on Cortana.