In today's Commander Banned list announcement, no new cards were banned. Instead, the way Commander's interact with the library has changed.
Previously a Commander acted as normal if returned to its owner's hand or placed into his or her library (this act was known as tucking the Commander). This is no longer the case. Now, if a Commander would be returned to its owner's library or hand it can be moved to the Command Zone instead as a replacement effect. If moved to the Command Zone, the Commander Tax applies.
The reasoning behind the changes can be found in the original post. The main points are:
As with other rules changes, reactions have been mixed.
I'm in favor of the new #CMDR tuck rule changes. My Skullbriar deck is even happier than I am.— CMDR Decks (@CMDRDecks) March 24, 2015
The #CMDR rule change I want to see is the elimination of Commander damage. It leads to feel bad games. No Commander kill is cool/fun.— Brian David-Marshall (@Top8Games) March 24, 2015
When someone told me you could shuffle your Commander into your deck, I thought it was stupid. I'm glad the rule isn't stupid anymore.— Brian Kibler (@bmkibler) March 24, 2015
How does this change affect your favorite deck? What effect will it have on your latest round of updates? Magic is nothing with change and this is another in the lineage of the game.