The IEEE seems to think that it increases range.
http://standards.ieee.org/announceme..._ratified.html
IEEE Ratifies 802.11n, Wireless LAN Specification to Provide
Significantly Improved Data Throughput and Range
https://docs.google.com/viewer?url=h...ts_systems.pdf
"under development for the IEEE 802.11 standard
providing a marked increase in throughput (from
20 Mbps to around 200 Mbps, in practice) as well as range
of reception (through reducing signal fading) over the
IEEE 802.11a/g standards currently in use. Multiple anten-
nas, or MIMO (Multiple-Input, Multiple-Output), is the key
innovation used to obtain these benefits."