Not only am I smart enough to work it out, I’m smart enough to know that all else being equal I’d prefer not have to work it out, and that this preference doesn’t make me insufficiently smart to be working on a computer. I’m also smart enough to wonder if someone who would presume that someone who might prefer not to have to work something out, even if they are smart enough to work it out, is not smart enough to work on a computer, is smart enough to be working on a computer.
USB devices are interrupt driven as well (the USB host controller has an IRQ assigned to it). This usually isn’t an issue.
All USB devices on one “network” share the total bandwidth of the bus. If you’ve got a “bus hog” like a disk drive or network controller, then it is going to use up a lot of your bandwidth on that bus. If performance is an issue, you can segregate your bus hogs to their own dedicated networks so they don’t slow everyone else down.
Flash drives only use up bandwidth while you are accessing them. Just plugging in a flash drive won’t necessarily slow anything else down, but if you are transferring files back and forth, or if you are doing something like running firefox off of a flash drive, then you may see some performance issues if you have other high bandwidth devices on that bus.
Thats your problem and thats not a problem with USB but with how the manufacturer designed your computer. I usually see 6 in the back or rarely 4 in the back with two in the front.
One minor reason is that you can just do more with USB - so you can have a keyboard that incorporates a trackpad*, or a USB hub, or other kinds of external devices.
*It might be possible to do this with PS/2, but with USB, it’s bound to be easier to implement.
With USB, you have two peripherals plus a hub sharing the keyboard housing. As long as power isn’t a huge concern (it won’t be) that works perfectly.
With PS/2, I can only imagine it would be a huge hack involving hardware and software.
The USB keyboard standard also has a lot more keys defined. If a manufacturer wants to ship a keyboard with a F13 key, a HELP key, and an UNDO key, they don’t need to define their own signaling codes and ship a custom driver. It’s already there in the standard, and ready for use.
I actually have a F13 key on my keyboard. It’s potentially awesome.
F13, eh? I bet your volume control goes to eleven too. 
FIE on the F13 key
My Apple USB keyboard goes up to F16. 
BFD. My 16 year old ADB keyboard has F13, F14, and F15 on it.
My beef with PS/2 is that since the connector is round, some users would insist on trying to screw in the connector to the port.
It is possible. The one sitting a few feet from me (it’s not my regular keyboard, mind you, just something someone was getting rid of and somehow made its way here) has a PS/2 port for the keyboard functions and a serial port for the trackpad functions. Remember serial mice?
Many USB keyboards also function as hubs where you can plug in your thumb drive and dongle for your wireless mouse.
My ancient Gateway AnyKey keyboard has an extra set of F1 to F12 on the side, angle keys on the keypad, and the programming keys. I’d love a replacement that had useful keys like that instead of those dumb multimedia and Internet keys.
And yep, I remember serial mice. Heck, the ancient computer in the lab when I was in grad school (we used it to run an equally-ancient UV-Vis) had a serial mouse. I think it also had full-sized boards. That took me back.
As for the USB ports in keyboards, my experience has always been with the older Mac ones. I can never get enough power out of one to run a thumb drive, though it’s enough for a mouse
Ok, to summarize:
It’s cheaper to have 1 type of connector rather than specialized devices for your keyboard, mouse, printer and whatever. A win for consumers.
USBs are hotkeyed, which means you can remove them while the computer is still on without toasting the motherboard. You remove a PS2 connector from a powered computer at your own risk. Another win.
Four USBs are pretty compact, which is nice for laptops.
USB 3.0 ports are scheduled to be released in December. They may be 10x faster than USB 2.0, which was faster than the earliest generation of USBs. They will be downward compatable.
All that said…
I wanna 6 in back and 2 in front.
USB hubs don’t always work that well. A cheap plastic hub combined with a USB extension confused Win2000, so I couldn’t conveniently set up an antiquated computer with a flash drive. More recently, Vista wasn’t able to deal with my keyboard or mouse when they were connected to my LCD monitor’s hub, though the USB printer handled the hub just fine.
I bought the PS2 to USB converter linked to above and it works fine. However, it also typically takes up 2 adjacent USB slots.
Of course there’s also the premature obsolescence of keyboards, mouses, printers, KVM switches and whatnot, but that can be taken in stride.
I’ll have no problem if they replace the PS2s with extra USBs. I need at least three “free” after mouse, keyboard and printer.