Apple is offering a $1.99 downloadable upgrade to enable 802.11n on various Macs. Every Mac with an Intel Core 2 Duo processor or Xeon processor (iMac, MacPro, MacBook and MacBook Pro) has been shipped with 802.11n capable hardware sitting inside waiting to be activated.
With the announcement of AppleTV and the Airport Extreme (both 802.11n devices) it was also declared that Intel Core 2 Duo machines (iMac, MacBook, MacBook Pro) had already been shipped with 802.11n capable hardware which simply needs a software update to enable its functionality. Apple kicked up some controversy by claiming that due to accounting regulations they have no choice but to charge customers for the software upgrade. It's undecided as to whether or not this should be the case—on the one side accounting gurus claim that Apple have no choice but to charge, on the other side MIT's LaFond said "There's absolutely nothing in the GAAP requirements that says Apple must charge its customers for that software upgrade."
The excuse seems pretty weak to me, we don't pay for BIOS updates which add new functionality nor for Windows updates.
I bought the Enabler from Apples online store. I'm a little annoyed that in the UK we have to pay $2.45 rather than $1.99, it's not much but its the principle and Apple always charges European customers more (and for a software update there is no additional transport cost etc). That said $2.46 is a small price to pay for an 802.11n upgrade. It's certainly cheaper than buying new hardware.
Those who aren't inclined to pay for the update will most likely still update thanks to their local torrent site.