Finalisation of 802.11n is still reportedly over a year away. There is of course no guarantee (actually, little likelihood) that any of the draft-n gear available now will be upgradable to the standard, when it comes.
The conventional wisdom for using draft-n equipment at the moment is to get all the pieces from the same manufacturer, to make sure they work together as intended. But that's not always possible.
Have any of the computer or networking magazines, or any of the consumer-protection testing labs, run any studies comparing how well (or how poorly) 'mixed' environment networks run? Things like 'The A pcmcia card works with B's router but not C's access point, while D's pci adapter works with routers from A and C but not B', etc., etc.
Given that there are only, what?, four or five or six major manufacturers of consumer- and SOHO-level equipment, it shouldn't be too hard to put the more popular models through their paces.
cheers,
Henry