Only take these if you are confident the laning phase will be easy and you won't take much damage from your opponent.
If you want to be cheesy with AP instead of defense but are not confident in your laning phase, you can take AP/level runes so that you will have a powerful ultimate at level 6 .
Update: With the recent patch, mr/level runes are superior to flat mr.
They equal out with the flat runes a bit earlier now, so you can usually get away with them.
You give up only 2.25 magic pen and in exchange gain 8.1 armor pen.
Auto attack harass is an important part of your laning phase.
Hybrid pen also makes it slightly easier to last hit as minions do have armor values.
However, they are much more expensive in terms of their IP cost, so if you can only afford/own Magic Pen reds, those are perfectly acceptable.
Good example matchups for possible barrier usage are Lux, Fizz, and Viktor.- Not a bad choice with a coordinated team as your utility and burst can easily lead to kills at your teleport target (especially with homeguard), but I don't like to take this in solo queue as random allies don't always ward properly to setup teleport plays.
Hybrid Pen Reds - Hybrid pen is the best choice for reds.
Even against AD opponents, it seems right now that taking a set of 4 armor yellows and 5 flat health yellows might be the best choice (though I have a page setup with all flat health yellows and armor blues if there isn't much magic damage).
Movement Speed Quints - I personally believe movespeed is essential on .
However, if you are playing against a champion that can bully you in early levels, take flat MR so you can trade (examples: etc).