Regarding 3e stat blocks: I really learned to hate them the longer we played. Eventually, I developed a shorthand to add all the information required to play a monster without requiring any lookup during play. But it took me _hours_ to create some of these stat blocks. And I still had the problem that e.g. for high level spellcasters I'd end up with stat blocks that didn't fit on a single page. This lead me to use colouring to high-light the important parts of the stat block and add a (separate) tactics section detailing the powers most likely used in the first couple of rounds. I really don't want to go back there ever again!
Because it's page flipping, and - often - they'll refer to two stat blocks in very different parts of the book. Having to flip between "Zombie" and "Orc" all the time in one encounter isn't that enjoyable.
Yup, that's the one disadvantage: Either encounters have to be restricted to only use monsters that are on the same two-page spread or you have to provide the stat blocks separately in some way...
Having the statblocks in the appendix sometimes works. However, we're still talking about the problems of space: every long statblock eats up the available page count of the product, reducing the space that can be used for the actual adventure.
I really liked what they did for 'The Red Hand of Doom': The monster appendix was released seperately as a pdf! Why did they abandon this excellent idea afterwards? Probably in favour of the delve-style encounter descriptions.
I'm not a fan of condensing 4e stat-blocks as I think it would make them less readable. Using a lot of abbreviations and/or defined terms would counter the goal of not having to memorize anything and having all the required information in one place.
For, say, 90% of the monsters using monster-cards would work: You can usually fit the complete stat block on them (although it might take both sides of the card to do so) and you can arrange them any way you like and still see all monsters participating in an encounter.
Printing stat blocks from the DDI compendium works well too, for much of the same reason. And if WotC manages to provide a useful, working monster builder again, this will probably be the best possible approach:
When DMing a published module I often fiddle with monster blocks, level them up or down, add monsters to encounters or turn solos into elites, etc., etc.
Right now, I typically just pencil in the required changes, but being able to make the changes comfortably in a software tool would clearly be preferable.