My brother had a computer which started up in about 6 seconds and he didn't even have an SSD ... just an overclocked AMD quadcore running at 4 GHz ... until he changed some hardware and then it took a lot longer, he was pretty frustrated about it. I don't remember the details, but I agree with starkers here: it is possible, with the right hardware and a bit of luck.
My windows computer at work also has a good hardware set-up, it also takes little time to get to the login screen, and also very little time to load the desktop after that. My boss is good with computer hardware and chose a good setup. This one has an SSD though, that helps of course.
Compare that to my computer before I had the SSD. Startup took almost 1 minute. Then the login screen. The further loading of all kinds of drivers and shit, it took another full minute before the computer became responsive again. Total load time was about 2 minutes... I was about to throw my computer out of the window, that's when I bought the SSD and now the load times are ok again.
Or maybe it was because my HDD was dying... it has more or less crashed by now, I cannot start up with my original HDD included for some reason. Or maybe my motherboard is dying or maybe the cables are crap ...
Who knows... it's a mysterious world sometimes.