John Gruber talking about if the iPad replace or not a Laptop. Actually he was responding to Eric Grevstad. Grevstad assure iPad is not a Laptop replacement, Gruber says that "In the real world" he sees more and more people using the iPad where before a Laptop was needed.
To me a tablet does not replace a Laptop, but that is only because I like to have too many apps installed in my Laptop, specially developing, and server apps, because I like to learn about them. But for the normal job, read and answer emails, read the news (RSS), use Twitter, the like. Yes an iPad, actually any tablet or my iPod Touch can work.
Before the smartphones era, I used to travel with my Laptop, I had meetings all day, and at night when I have arrived to the hotel, I used to turn my Laptop on, and read and reply emails. Now a days I do that using my Android, Blackberry or iPod. I only turn my Laptop on, when I want to write long, or when I want to "play" with my "toys" configuring servers, learning about Unix, Linux or Mac OSX.
So, for a lot of guys the iPad indeed replaced the Laptop, specially the "travel laptop". Just like Gruber said:
That the iPad is not a substitute for a laptop for everyone does not mean it is not a substitute for anyone