I haven't used one personally, but having read a few reviews I feel that unless you really need the speed boost (for local networking) or have issues with coverage or interference, the price premium over 802.11g may not be worth it. You will also have to buy the matching PCI/PC cards as well.
It could be the redbull that i drank last week, but is it me or is technology upgrades often reminders of how useless R&D can be. You think with MIMO you actually recieve a noticeable increase in communication speed rather you get a increase in price rather than bandwidth.
-- The best upgrades in technology come from people who learn short cuts to current technolgoy--