After being completely pissed off with ubuntu's boot time I've installed Gentoo, just to check whether it's me or ubuntu - with parallel boot in openrc my gentoo fires up in 10-15s. Then I've turned on verbose upstart and disabled plymouth (just to see what happens behind the scene) and I saw services constantly going up and down during the boot process, reacting on some events, triggering other events - that is to say making complete mess during the boot.
Hence I'd say replacing upstart with whatever else can really have a big impact on boot time.
P.S. kernel bootstrap time (time lapse from grub till (pre)init) on both kernels is about 7sec, although ubuntu is with initrd and after kernel boots it passes control to boot-* scripts in initrd, which takes another 3-5s, and in gentoo I compiled monolithic kernel with all required modules (except optional) compiled-in - hence without initrd.
I run a monolithic kernel too, everything I need is compiled in things I don't need are not compiled at all, I only have about 4 modules which makes for a nice quick compile time when you're following git master and very quick git-bisects
Count me in the list of people that apreciate fast boot times. For all I care boot time should be 3 seconds since I turn on my computer. When I turn it on I want to use it straight away. And no, suspending is not an option because that uses some power. Hibernating is actually slower (on resume) than a cold boot. I wonder how meego can get such awesome boot times. Last time I checked it was taking 30 seconds on my crappy Eee pc, and that's when running from an old and slow USB stick.