Even though the weight change is quite small, everyone reviewing it has said the feel of the thing is completely different. It feels lighter but sturdier and sits in the hand differently. Don't think they can get the weight down much more without breakthroughs in battery tech though, since that's what makes up most of the weight.
As for how 'necessary' the iPad is, I could dredge up a lot of posts by others on other (non-Apple!) forums where they couldn't live without it. These are typically either family homes where the main computer isn't in the living room, older people who find the screen of phones too small and fiddly, and for people who commute and want some basic entertainment/productivity stuff without the clunkiness of using a netbook. Some of these people were sceptical initially but found themselves increasingly not bothering to turn their computers on, or having to prise it from their children.
I wouldn't buy one till I was commuting into London for a job (here's hoping!), but even at home I would rather build up an iBooks collection to read on it, replacing my physical books, use it for browsing in bed or downstairs when I'm with other people rather than hiding in my room, as a better remote for Airplay e.t.c. Of course I can do all this on my phone, but by the same extension I could do all of this on my computer as well, it's just nice being able to do it on something that weighs nothing but is pretty powerful and has a big enough screen to read books comfortably.
