None. I dislike the form factor enough that I'll stick with an old-school desktop machine at my usual place of work and my phone/tablet anywhere else. If I need

None. I dislike the form factor enough that I'll stick with an old-school desktop machine at my usual place of work and my phone/tablet anywhere else. If I need to do serious typing-type work somewhere else, the destination (client) will no-doubt provide. I've never noticed the lack, and it makes getting through airports a bit easier.