Well, it's certainly out in the UK now, and I've got a copy.
In the earlier poll about whether one would purchase or not, I think I said "I look at it and decide if I think it is worth it". I flipped through it and decided it was.
I've just finished reading it, and I'm happy that I made the purchase. I like the background to the design process, I like the races and classes information... No - more than that, I want to play a character of each of the races - and I want to play a character of each of the classes too! Arrgh!
It is a shame that some of the class write-ups are a little slim (ranger & warlord I'm looking at you - especially since rangers didn't get the thought they needed at the time in 3.0 and had to be revised thoroughly in 3.5, and warlords are so new in their leader (aka healer) niche that they would have benefited in as big a write-up as the warlock got for sure. I like the ranger characterisation as 'guerilla fighter' though)
It is interesting that they include sorcerer and druid in the class descriptions here even though we are pretty sure that they are not going to be in PHB1. Since I don't think I saw anyone else mention it, I'll just say a bit about the druid from here:
Druid
The current design for druids allows them to select wildshape a lot more often, but at a price(?). Druids select shapes they can assume in much the same way that other classes pick spells and manoeuvres {so presumably they may have 'at will', 'per encounter' and 'per day' shapes}. They designed different forms for different needs - hawk for spying, mouse for sneaking, bear for tearing the orc king apart. To give an incentive to walk around in human form there will be a selection of nature themed spells to give some utility and ranged attacks.
Stand-out comment
One comment from Mike Mearls which stood out to me (amongst many stand-out comments throughout, I hasten to add), is one which gives me particular delight.
"As a rule, immunities are almost completely gone from D&D 4e. In their place we have damage thresholds to reflect resistances and invulnerability. A fire elemental might ignore a wizards fireball, but an elder red dragon can still blast it into oblivion with its breath weapon"
Huzzah! I've always hated outright immunities, and I think this is an excellent development. Long may it stand! BTW, the above comment came from something about sneak attack, how almost everything now has some vital points that can be attacked (e.g. joints on a construct).
Art
I love all the art direction, with two exceptions.
1) I don't like spurs on all the humans, I think it looks silly and would probably be hugely inconvenient; the assumption that humans live on plains and use horses is an OK one (although in honesty they ought to be riverside and coast dwellers too - plains are notoriously poor terrain for farming and everything else), but I don't think it means that we should see spurs everywhere!
2) Halflings. Almost all the halfling pictures are indistinguisable from humans because there is typically nothing for scale. The best picture is probably of some halflings on a boat because the angle of the picture is looking down on them. My 2cp for the art direction

)) is to ask to have more of the halfling pictures displayed from a humans eye level, i.e. looking down towards them a little. This would visually accentuate their stature in a way which is seriously missing at the moment.
Cheers