PC World's advice: go MIMO if you need range: A very sensible array of advice from Becky Waring over at PC World based on testing several of the current MIMO (multiple-in, multiple-out) Wi-Fi gateways and adapters on the market. Waring offers the same recommendation that I have, which is that for homes or small businesses for which the price premium overcomes the cost and/or hassle of installing many individual access points, a MIMO gateway makes a great deal of sense.
I would add that for networks in which throughput over Wi-Fi is a significant issue over short distances (up to about 50 feet), MIMO is the only technology on the market that can increase throughput even with existing 802.11g cards to their highest level at their greatest distance.
If you don't need range or speed and adding access points is not a big deal--you have Ethernet installed throughout a house or office or understand how to configure Wireless Distribution System and can deal with its limitations--then the price premium is probably worth sitting on your wallet as the cost of this technology drops rapidly because of unit sales and competition.
Meanwhile, Mobile Pipeline's editor writes about MIMO's early use in business: It's not ready for the enterprise yet, but even consumer-scale and early small-office MIMO gear has unmistakable benefits in certain cases that Haskin lists.