For starters, tokens can’t block Void Winnower, due to tokens having a 0 CMC. According to a ruling from Wizards, 0 is considered even. Mathematical debates aside, it’s going to be fairly tough to chump block this guy. Then again, plenty of removal is at odd converted mana costs, so there are definitely ways to deal with this behemoth.
What Void Winnower seems best at is being a metagame answer to the big even converted mana cost spells in Standard. At the time of Void Winnower's release, these were Ugin, the Spirit Dragon at 8 mana and Ulamog, the Ceaseless Hunger at 10 mana being the chief concerns. With Eldrazi Ramp a legitimate deck archetype, especially in Modern, Void Winnower is certainly a legitimate candidate for sideboard play. It can randomly hose a number of decks if their key cards have even converted mana costs.
In EDH, Void Winnower is a “just say no” card that will lock some Commanders out of the game. It’s a pretty mean card in the format. While someone will probably find an answer to it in a multiplayer game, it will wreak havoc while it remains in play. It may come down to using Swords to Plowshares on it and gaining the owning player 11 life. The fact that it can help your team get through for extra damage is also another big consideration. Because it's colorless, Void Winnower can be included in a wide variety of decks.
Naturally, the Commanders that will want to use Void Winnower the most are those that can sometimes cast him for free (Rakdos, Lord of Riots and Animar, Soul of Elements) or cheat him into play (Mayael the Anima and Jhoira of the Ghitu). But pretty much any deck can make use of Void Winnower if you can somehow get him into play on the cheap. Because he doesn't have an on-cast trigger, he's actually a big threat and always worth putting into play no matter how you do it.
While he may only be a $2 card for most of his life in Standard, there's so much demand from casual Eldrazi deckbuilders and both kitchen table and competitive EDH players that Void Winnower won't stay cheap forever. He's definitely a keeper.
How would you use Void Winnower?