I'll further edit this, day by day.
Comment: I don't have the same amount of data on my different readers. On Kindle DX, for example I only have about 150 books so far. Indexing more files may change the measurements a bit...
Kindle DX:
Startup : 5 seconds, spectacular. No idea, what's their "trick".

Maybe it's suspend-to-ram instead of really turning off or something like that?
Startup from Standby : < 1 second, can't even measure it.
Kindle 2
Startup : 7 seconds, still benchmark

Startup from Standby : < 1 second, can't even measure it.
iRex iLiad
Startup : 45 seconds
Startup from Standby : No standby, I very often simply leave it on.
iRex Reader 1000S
Startup : 50 seconds
Startup from Standby : No standby.
Cybook Gen3
Startup : 35 seconds
Startup from Standby : No standby.
Sony 300
Startup : 30 seconds
Startup from Standby : < 1 second, can't even measure it. 5 seconds when indexing my library.
EDIT: Just took 72 seconds to "cold boot". Way more books than the first time and way more fragmented collections structure.
Sony 505
Startup : 45 seconds
Startup from Standby : < 1 second, can't even measure it. 5 seconds when indexing my library.
Sony 900
Startup : 45 seconds
Startup from Standby : < 1 second, can't even measure it. 5 seconds when indexing my library.
No recognisable improvement to older units (not necessary, has been fine already).
I'll check why it has been slower than Sony 300. Have to compare number of books, indexing fro new books and so on...
EDIT: Just did compare to Sony 300. Sony 900 is a bit faster for the same amount of books.
nook
Startup : 70 seconds.
Startup from Standby : 2 seconds, almost instantaneous.
The others will follow shortly. I'll add times for page turns as well.
Anything else I should measure?