The Question: is Censor good and/or relevant in Modern?
Positives:
-extremely cost effective
-almost never a dead draw
-minor tactical advantage (deck thinning)
-non-type conditional counter
Negatives:
-extremely limited stopping power
Discussion:
So, plenty of decks want to have a turn 2 answer to what opponent is doing and/or buy some time to get your win condition ticking. Censor does both, with an interesting twist.
In the early game, its a deadly counter as opponent's mana production is limited, and censor doesn't counter any specific type of card (I.e. like negate, spell pierce, spell snare, etc.).
In the middle game, its not as effective, but still a decent threat, and can be used as a double stack once opponent tries to respond to something your doing, or responds to your response, which eats up his mana in either case.
In the late game, when opponent has enough mana to not have to worry about it, cycle her off for U at instant speed with a smile on your face.
So, what I'm contending is that in a deck that wants retroactive counters, 4 censors is basically never a bad move as you get SOMETHING out of it in the opening hand, middle game, and when top decking.
It's also interesting to think about Censor in the context of the other cards that would tend to group with it.
Remand, for example, is a contemporary to Censor that realistically works together beautifully. Running 4 copies of each basically guarantees that you have a turn 2 tempo eater, which is PRECISELY what a hard cast control deck wants.
It even offers an interesting option with Snapcaster Mage, as for 5 mana you can cycle Censor and snap it back, which is a +2 material with tempo combo (of note, this combo works well against grave extraction problems).
Feel free to comment, disagree with me, or what have you. Just trying to kick around ideas.