I was against this for years, but slowly came around to the concept after umpires continued to butcher one important call after another that could easily be corrected through a review. Now an expanded version has arrived and I like it a lot!
I just watched the Cubs-Pirates opener on ESPN, which included an overturned call on a pickoff play in the top of the 10th. The Cubs' Emilio Bonifacio was clearly out, but was originally ruled safe. Umpires have long ruled in favor of the runner on extremely close pick-off plays because it's one of those instances where they had to be certain they were right before throwing up the thumb. The default call was always "safe," and a lot of guys remained on base who shouldn't have.
The process was completed quickly – it took much less time than your average NFL challenge. I really think it's going to be a great thing for the game.
What say you people?