EXPERT RESPONSE
As of mid-2006, draft 802.11n products are improving but are not yet mature. Earlier proprietary MIMO products were aimed at residential users who wanted better speed and distance, but who were not significantly constrained by multi-vendor or forward compatibility needs. In short, proprietary MIMO was beneficial only if you bought your AP and cards from a single product line.
Today's draft 802.11n products are doing their best to comply with the emerging IEEE standard, trying to get a jump on the market that will materialize when the standard is finalized next year. But, strictly speaking, there is no such thing as complying with a draft standard. Vendors that align products with a draft are gambling that significant problems will not emerge before the standard is fully baked. In particular, interoperability issues are likely to crop up during "plug fests" held for that very purpose. Best case: all changes end up being resolvable by firmware upgrades. Worst case: changes turn a few draft 802.11n products into non-interoperable doorstops. At this point, you just cannot know for sure. However, a benchmark test of early draft 802.11n products conducted by Farpoint Group in May 2006 found numerous interoperability problems (see PDF).
If you can defer your upgrade until end-2006 or early 2007, you will be able to buy 802.11n-based products with a much higher degree of confidence. Few enterprise-grade draft 802.11n products are shipping today anyway -- product selection and price will improve if you can wait a few more months. If you cannot wait to invest in new hardware, look for enterprise APs with field-replaceable components that provide a predictable upgrade path from 802.11g to 802.11n. Don't forget that you'll need a plan for upgrading clients too, when Wi-Fi certified 802.11n products finally emerge. For on-going news on this topic, see Glenn Fleishman's MIMO+N News page.
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