I just replaced the stock OEM hard drive on my 2010 macbook pro 15 inch with a Samsung 840 Pro SSD 256GB and installed Yosemite on it from scratch with USB (the first time i am using Yosemite). Now when i boot my macbook pro up it takes about 5 seconds to get from powered off to the log on screen, but then when i enter my password it shows a loading bar that slowly fills and my user icon changes to an apple logo. Then after about 20 seconds it logs in. Moreoever the log on screen is gray with the user icons, which is not my background on my account. But if i log in and then log out it changes the log in screen to be my desktop background.
This is a big change from my old mavericks where it took longer to boot up but instantly logged me in. I thought SSDs had super quick boot and log in times.
It shows the quick boot to log on screen with the strange gray background, me logging in and having my icon change to an apple with a loading bar under it, and then me going to a website, and logging out, notice that after i log out the log on screen changes to my desktop background. And then i log in again and it goes quickly unlike the first time.
After doing a restore via the net with cmd Option R it seems to be booting normally