First, some reminders about Internet and Network speeds.
Most cable connections to the Internet run between 8 - 12 Mb/s (aka Mbps - Megabits per second). DSL is about the same at the high-end, if you are lucky enough to have fiber-optic, you might get 20Mb/s.
That being said, do you ever get 8-20 Mbps of download speed? No. Just No. The websites/download sites are capped on their end as to how fast they will feed you data. That is why downloads are not instantaneous. Many download are very quick, but the speed is still regulated by the site.
A - no one uses A.
B - 11 Mbps
G - 54 Mbps
N - 300 Mbps (approximately - N standards are either still in Draft mode, or very recently become official)
N+ - BS
Notice how even B exceeds most capabilities for Internet connections.
What I have done with B/G in my house:
Simultaneously: multiple torrents downloading on multiple computers, streamed near-DVD quality movies from Netflix, played MMORPGs, chat, surf the net.
Back to the offensive part:
Best Buy/Geek Squad has a poster by the WiFi routers proclaiming that
G is good for general Internet
N is 'adequate' for streaming music, movies, games
N+ is really what is want for streaming movies, music, and games
WTF?! N is adequate? Yeah, for a definition of adequate like getting 80mpg is adequate for a car, or how the Bugatti Veyron is an adequate sports car (0-60 in 2.46s, top speed 253mph).
So, if you really, really push to max out your incoming pipe (assuming you have fiber), you still can not saturate your G wireless, unless you are trying to maximize your connections within the house (like say copying blue-ray disks to and from multiple computers while surfing, downloading, streaming music and videos and games. So, if you really have to try to saturate a G network, how the fuck are you going to possibly saturate an N network today? Yeah, didn't think so. Adequate. Dumbasses.
edit: fix typo