This says more about OS X than it does about SSDs. I have two Debian boxes. One has an SSD. The other has a regular disk. They both boot up almost immediately.

The reality is that reading about 323k into memory is fast from both SSDs and rotational disks:

    $ ls -lh `which gdm`
    -rwxr-xr-x 1 root root 323K Sep  5 14:20 /usr/sbin/gdm