For me it takes exactly 14 seconds.
My hardware is pretty fast but I have plugins: Waves 7 complete pack, Line 6 complete pack, Groove Agent 3, Halion Symphonic Orchestra 1.5, IK Multimedia T-racks 3, Sony complete plugin pack (that came with Sound Forge 10). Those are slowing it down a bit (I mean the startup).
Anyway, not too long I think. Some of my projects startup for like half a minute or so.
All I have is Absynth 4 and Battery 3. C6 takes about 5-8 seconds to load.
Despite running on XP, I find that C6 takes no longer to get going than does C5.
My DAW is not especially fast. The main program takes 32 seconds to load, projects 10 - 30 seconds depending on what’s what.
HOWEVER - let’s see what happens when the clocks go forward at the end of the month? 
64 seconds.
22 seconds
18-20s
20 secs ish.
Waves Complete 7
Sonnox Elite bundle
Lexicon PCM Native
SoundToys bundle
Native Instruments Massive
13sec.
10 seconds for me,
but is really depending on how many plug in’s need to be checked, I have a lot of plug ins (UAD mono & stereo), Powercore, Vienna Suite, Komplete 7, AVOX, Vocaloid etc, and if I don’t have the iLok in, then the EW choirs plug in complains at boot up, so it is checking things at boot up you are not expecting.
After som cleaning and rearranging it takes 24 sec. to start Cubase 6
12secs from clicking the button to have a small project open from my recent items list.
Win7, Cubase 6 (64bit).
I don´t care. (perhaps 10-20 sec?)
Computer (and cubase) boot in the morning and shut down at midnight (or often later).
Cubase is very stable on my system, not necessary to restart.
Therefore the cubase project load time is more crucial for me - and this is of course very different from song to song. understandably.
20-24 seconds