MIMO is cropping up all over: NetGear is the latest to announce a MIMO (multiple-in, multiple-out) product. They're partnering with Video54. Linksys has apparently chosen Airgo. Samsung and Athena announced single-chip silicon yesterday.
The near-term problem with MIMO isn't with the technology itself, but rather the non-standard higher speed modes. No one is claiming interference, but these modes won't be certified by The Wi-Fi Alliance or any other group. That means interoperability, even among devices made by manufacturers using the same silicon isn't assured.
The worst part, in my estimation, is that this generation of MIMO technology isn't what the final 802.11n specification will look like. So purchasing MIMO today except for specific applications in which you need substantially higher throughput and range from a single device over interoperable, certified 802.11g means you're buying a dead-end device.
802.11n might achieve speeds of several hundred megabytes per second, and there's is practically a total certainty that the final 802.11n won't be just a firmware upgrade, but rather a difference in both hardware and silicon compared to today's MIMO devices.