I have a hard wired Blu-Ray player and XBOX 360 but the Wii, handhelds and even my HTC cell all work well off of G. I've hosted 12 player Mario Kart Wii over G without any issues. I think it has a lot to do with my upstream though and really knowing how to configure the router currectly with and/or without QoS. I hardly use even close to half of the range so lower end models missing more than half of it isn't a big deal for most.
If I ever go wired for everything, I'm going to need an 8 port version of the the DIR-857, which brings me to another point. Why aren't the high-end models like the new DIR-857 available in an 8 port version? With 2 desktops, 1 notebook, an XBOX 360, and 2 Ethernet enabled Blu-Ray player for YouTube and NetFlix. I'd like to have all of those wired without having to put a switch in. The Wii, Brother color laser printer, HTC phone, DSi, and 3DS would all still be fine for WiFi implementations and I could actually setup more of a home server instead of storing the stuff on local systems.