[lowercased]

When you interacted with a 'computer' once or twice a week, perhaps... seeing "please" is ... neat? A 'wow' factor ("wow! It knows English!")?

Peppering input fields and forms and folksy welcoming language scattered thoughout might be useful now and then, but for systems where people are using it repeatedly hourly/daily/weekly... it's (at best) clutter and noise.