Can you take a screen shot of your login items under system prefs/accounts? That may speak volumes for what is causing the slowdown. Also, define startup. Is it the time it takes from cold boot to when everything is loaded or the time it takes from cold boot to the time you see the gray apple on the gray screen (this seems to be something people get confused with).
This has been annoying me too, since i installed 10.6 my macbook takes around a minute to boot, from the time i hit the button to when i see my desktop. when i first got it, when i had 10.5.4 - it booted up in 30 seconds flat.
I've had the same problem when I took the HD out of my MB Pro (that I sold) into my MB. MB would take over 1 minute to boot. Thanks to the forums members suggestions I reset PRAM, now it boots in 35 seconds.
Yeah, I suggest you to reset your PRAM too like excommie said. You can do that by pressing command-option-p-r at your boot up. Keep pressing until you hear three diing sound, then let go of it... that is what the youtuber said... I tried... it didn't make so much difference. by the way, I have 10.5.8 leopard. I wish I had snow leopard like yours.