Sharing a WiFi access point among too many devices can shut down access for everyone. At some point, the high congestion levels overload the WiFi router, making it in effectively useless. This isn't a common problem for home networks, but it does occur (frequently?) for events such as legal conferences or when you stay at a hotel.
An interesting software solution from NC State Engineers looks to be on the horizon. It's called WiFox and based on tests of 45 concurrent connecting devices, reported a 700% speed improvement, and a 30-40% reduction in network latency. The performance increase comes from stopping the WiFi router from giving equal channel priority to both incoming and outgoing data. When congestion levels get high, the device focuses almost exclusively on local requests, which clears out the backlog before addressing the inbound data traffic.
Perhaps the best part is that this technology can be rolled out within your WiFi router's firmware. Not that it's available right now, but because it's entirely software driven, it shouldn't take very long to come to market. And it won't require you to purchase a new WiFi router.