I haven't read this thread that thoroughly, but as far as I know it's a case of:
Boot > use Metro (which takes some getting used to, as with all new UIs), OR
Boot > Win+D > business as usual, with Start8 as an optional extra.
The second scenario is usually even more similar to older OS, if you consider what most people do when booting their PC :
Win7 : boot/login > automatically get to desktop > click on your favorite shortcut (desktop or task bar) : Firefox, Steam, Word, whatever
Win8 : boot/login > automatically get to start screen > click on your favorite shortcut (tile) : Firefox, Steam, Word, whatever
It's only a matter of aesthetics, functionally it's the same process.
It's not faster as you have to wait for the animation to finish rather than it being instant.
The start menu has an animation too. I even edited the registry on my Win7 PC to have it toned down, and the Win8 menu still feels snappier.
And browsing all programs takes two extra clicks compared to Windows 7 and is much more cluttered if you have a lot of programs installed.
Hence the use of search function. I had mentioned in my first impressions that 8 is more search-oriented while 7 is more explore-oriented. It's a change that you may or may not like, but both work.
As a matter of fact, search is much more efficient when you have a lot of programs installed (navigating the Start program tree can become tedious, that's why we mostly use shortcuts to avoid it).
I've not seen or heard about any differences (except that you have to switch between the three sections instead of being able to see all the results at once). What made it inefficient?
Speed and relevance. If I hit Win > "cmd" on the PC I currently use, it starts giving me results after several seconds. If I'm looking for a file, it can take much longer to scan the folders, and rarely returns what I'm looking for (or it's so long that I get annoyed and explore the folders myself before it reached the right result)
Only if your programs have large easily recognisable icons.
Well, that's the point of an icon after all... And even small icons are enlarged when displayed in a tile. Those are customizable anyway.
Otherwise it's easier to just read the titles, and as Windows 8 has less room to display the titles, it makes it harder to browse.
As a matter of fact, the whole metro interface is more text-oriented than previous ones. If I remember correctly it's one of the rules of their "design language". Text is usually cleaner and more readable in Win8.
That's no use for desktop users though, unless they want to use a simplified email program designed for tablets.
And why wouldn't they ? Simple programs are no worse than complex programs, and in some situations they can be more convenient.