3D sound: adding "texturing" and doppler (and other) effects, 3D aural positioning, etc. I dunno if it was Creative who started it, but their EAX is probably the best-known 3D audio brand.
15 Amps is a lot, and while computers do suck a lot of juice and make your electricity bill nasty, you can go a long way on 15 Amps as long as you don't attach water boilers, microwave ovens, toasting machines, etc.
Count of USB devices is growing and growing. I'm keeping my own count down, but can see how it can be a problem. You don't
always have to power USB hubs; use a hub for connecting all the low-power and low-speed devices (mouse, keyboard, drawing tablet, cellphone data cable, ...), use dedicated ports for high-speed or high-power devices (external harddrives, etc.).
You can always buy a PCI card if you need more USB ports, the ones I've seen typically have max four external ports, since PCI cards can only be so tall. But some of them offer additional internal ports, that you can connect to front connectors, or they have "break out boxes"

Btw, if you're not downloading or connected to IRC or whatever, I suggest you use standby if you leave your box for 10+ minutes... resume from standby is really fast, and it does help on the power consumption.
If you haven't already, you might want to check
Tell me why I have to be a PowerSlave?, as it's related to this topic.