My dual-band Time Capsule (Airport Extreme) is handling my wireless clients without an issue.

1 MacBook Pro n 5GHz
1 PowerBook g
1 Mac mini g
1 iPod Touch g
1 Wii g
2 Squeezebox 3 (Classic) g

Before my wife took over using my PowerBook, it was also supporting her Windows POS Acer Notebook (802.11g).

I'm currently using my WRT54G with Tomato as a router in front of the Time Capsule and behind a cable modem. I'd be using the Time Capsule to route instead if it weren't for Tomato's excellent bandwidth monitor and to a lesser extent, its QoS (though I didn't have a problem with TC in this regard).