One of the complaints that I have heard about Linux is the slow start-up. I guess the way Linux displays the services that are starting upon boot up gives an impression that it is slow. Well, there is no denying that it is slow but not that slow compared to other operating systems – so there is definitely room for improvement.
Whilst I have not seen any "commercial" implementation of initng yet, upstart is taking center stage over at the Ubuntu camp. version 6.10 is now using upstart and I urge you to test it (there is a LiveCD anyway) and you'd be surprised at how fast it boots up.