These stuff never will replace a real pc for work unless you brag about google vs apple ot surf pages made for tablets or phones..
Of course not, and they're not meant to. They're limited-input devices made primarily for receiving and consuming media, they're not meant for content creation, and the available tools for creating content are limited and usually simplistic in nature. They're meant for quick changes and fix-ups, not for full-on usage as the only tool for a job.
My private phone is Android (Cyanogenmod), my work phone is Android, I used to own an Android tablet and I currently own an iPad Air that I got from a work-related course I'm taking. It would suck trying to do every part of my job on either of them, and I would hate to try it. But they're great for reading the news or catching up on mail while I'm on the bus, that sort of thing. I have a perfectly serviceable laptop, but when I need to check something, it's so much faster to just pull out my phone and look it up. Not to mention having Google Maps available at a whim, mapping really is the killer app for mobile devices.
As for the tablets, I usually bring it along to meetings etc. instead of lugging along the laptop. That way, I can quickly re-check previous mails if a specific subject comes up, or I can jot down quick notes with drawings and maybe show them on a projector if needed. With laptops, people have a tendency to almost hide behind the screens, a tablet is much more like an old-fashioned notepad in that you're not isolating yourself from the rest of the participants.