...although its grammar checking and automatic capitalisation could use some improvement...
Is it worth to buy an iPad just to read books? (I don't play games) and I think I can use my iPhone for chatting/writing emails/surfing online. Well, I can read books on my iPhone too (the text isn't smaller, books just got more pages then). Macs also support iBooks now.
I used my iPads a lot when I had an old Windows laptop as my only real computer. With my rMBP, the iPad just collects dust. If I am out and about, or in bed, I use my iPhone (as it can do anything my iPad can do). If I'm on the couch or need to do some real work, I use the rMBP.
The iPad has no use for me anymore. If they ever increase the size of the damn iPhone screen, I will have no use for an iPad ever again.
I prefer my Kindle Paperwhite for reading. My mini suffers from its low resolution.It just ended up being a glorified e-reader, and even that function has been replaced by a Kindle.
If iPhones grow to 4.7 or 5 inches, I really won't have much of a need for iPads at all.
Lately I've wondered if Apple has stubbornly refused to give the iPhone a modern sized display... just because it would cut into iPad sales.