Wireless has a definite place in today's networks, but it's probably not the place that most people have in mind for it. I'll elaborate on that shortly, but here's a few points where wireless hands-down loses to wired networks to get you thinking about this a bit:
1. Wireless Networks Aren't Scalable
There's two frequency (RF) bands for consumer wireless; 2.4GHz and 5Ghz. The 2.4Ghz band has 11 available channels, while the 5Ghz band has 23 available channels. What this means in layman's terms is that there are only 34 total wireless channels that devices can talk on before there is no more available airspace for communication without interference and cross-talk. I'll also mention that modern devices achieve the speed tiers for data throughput that they're labeled for by multiplexing throughput (basically using multiple channels at once for higher throughput). So if you're using only a single channel, you're limited to about 150Mbps as an absolute maximum data rate, and that's on 5Ghz only - 2.4Ghz is about 54Mbps.
2. Wireless Networks Are Highly Susceptible To Interference
A little backstory on the 2.4Ghz and 5Ghz RF bands. Those spectrums are classified by the FCC as "available for general unlicensed consumer use". Because of this, anyone with any devices can use these RF bands to transmit on since it's wide open for consumer use. Because of this, wireless networks and devices inherently conflict with each other since they're all fighting for the same transmission bands. It's not just wireless devices, either - microwaves, freezers, and other devices emit EMI on these frequency bands that interferes with wireless as well.
3. Wireless Networks Experience Natural Packet Loss
Gaming on wireless? Good luck. Most wireless networks suffer packet loss because data integrity isn't guaranteed on wireless - it's guaranteed by a high layer in the transportation process. This means that there isn't a way to assure wireless transmissions don't "collide" with one another in the air, and become distorted in the process, forcing the transmitting party to resend the data after a short interval.
Where Wireless Is A Good Fit
An ideal wireless network environment would be in an area with low natural interference, and with a minimal amount of devices on wireless - presumably devices that can't be plugged in to a wired network (such as cell phones).
A home environment with a small wireless router usually offers enough isolation from other wireless sources to offer good performance, and most homes have fewer than 10 devices on wireless, which is within reasonable expectations for ambient congestion.
Once you move into a normal apartment complex, things get more complicated (depending of course on the size of your apartment). Residents typically have wireless routers spaced closer together, causing more interference and crosstalk, as well as higher packet loss. I can speak from prior experience that even with a 1350 square ft. apartment, packet loss on wireless happened to a degree that online gaming was a lost cause on it.
Move into a tight-quarters housing environment (such as university housing), wireless isn't feasible anymore. Even with direct, 10-foot line-of-sight to an access point, your best bet is 3-6Mb speeds with a great deal of packet loss. There's simply too much contention in too small of a space, unless you line your walls with wireless-deadening metal.
In a business environment, your success will vary to the degree that you keep the wireless spectrum clean. Highly-populated coffeehouses and sports arenas will never have good reception due to too many devices in too small of a space, although you can probably get enough to pull up some web pages. On the opposite end of the spectrum, businesses with their own facility (not a leased facility, or a Suite shared with in a building with other businesses running their own wireless networks) will have a good degree of success with this, since they'll likely have an environment where they can control the level of ambient signal contention.
You can win with wireless, although you have to have a great level of control over your surrounding environment to do so. Since access spectrum is shared with all other ambient devices, wireless performance gets better the fewer devices are on wireless, and wireless should be designed around a mindset of keeping everything possible off of WiFi, and on wired media.
My own personal opinion of WiFi is to find an alternative wherever possible. There's too many uncontrollable variables in many environments to guarantee any level of performance on it. That being said, it has a definite place in networking today - just not the spot that it currently has in many environments.