I have a i7 2600 processor, 8Gb DDR3 ram, nVidia GTX570, and Ubuntu takes 45-50 seconds to boot and 32-35 seconds to power off, while windows 7 boots in 20-25 seconds and shuts down in 10 seconds. Both OS with autologin enabled, and in dual boot.

Ubuntu is slow with preload too, and doesn't show any boot splash after installing drivers and didn't recognize my nVidia graphics card on jockey GTK, I had to add x swat repository and that didn't worked. I installed proprietary drivers through terminal (nvidia-common, nvidia-settings) in order to have 3d acceleration. But it doesn't make any difference on the speed.

I also have a Pentium 4 PC and ubuntu 11.10 is way faster than windows 7 or XP. Also with nvidia graphics card and preload.

http://paste.ubuntu.com/924890/ there is my boot script, sorry but some words are in Spanish because my ubuntu is in Spanish. Not using WUBI, Ubuntu has its own partition, 64-bits, and Matlab 2011 has very low performance compared to windows version.