Your mating instincts will tell you whether someone
looks attractive the first time you see them. To deny that you have these instincts is to deny that you're human. Our instincts about this are essentially shallow, and they are powerful. Knowing someone looks attractive isn't always the same thing as deciding you want to boink them though, let alone date them.
Once you get to know them, other, more complicated parts of your brain can come into play and the person can then become much more or much less attractive. I can remember becoming repulsed by girls I initially thought were hot, and I've gotten hot for girls I initially didn't notice at all.
So overall: somewhat.
ETA: Then again, I suspect some people don't have a great deal of activity in those other, more complicated parts of the brain.