A friend of mine made a video comparing the MacBook Pro vs MacBook Pro with SSD. The video offers a good comparison of the boot up times between a MacBook Pro with a traditional 5400rpm hard drive and one with a solid-state drive (SSD). All the other factors were kept the same.
The conclusion: the boot time is approximately twice as fast on a Macbook Pro with a SSD.
Upgrading to a SSD may be a better choice for those who need or want a faster boot up. I hope this video helps in deciding whether to go with a SSD or a traditional hard drive.