I'm not saying they don't exist. I'm saying I've never seen ANY computer, PC or Mac, have issues with a device that was properly set up. Not complicated properly, mind you, but simply. Are any of the cases due to user error?
(Note: I work in a customer service job at the moment (hey, I'm a college student and it's easy) and nine times out of ten the customer is wrong. I'm not trying to be rude here, but a lot of people simply don't have very much knowledge about anything technical. The tenth person is a MacRumors member)
The USB Hub problem is a complete mystery and there is alot of discussion on this on the Apple support boards. There seems to be a problem with Mac Pro usb ports not working well with hubs and in some cases not recognizing them. I cannot, for instance, run a portable hard drive off my USB hub when using a Mac but I can when I am using a PC. The Mac will even recognize it though Parellels will which indicates this is a software problem. Similarly, there are issues with a bluetooth dongle I purchased for a fraction of the price of the bluetooth card. The official line from Apple is that they only support certain bluetooth devices.
Regarding the mouse, I went through a couple before I found one that works properly. Oddly enough, the mighty mouse was the worst. The pointer would be very shaky and float around on its own. The Kensington mouse did not have this problem. This is also a common topic on the Apple support forum.
I am fairly new to Mac desktops though I had been using a g4 notebook for years and thought I could just plug stuff in like I had for the PC. Unfortunately, I spend far too much time on support sites trying to trouble shoot issues. This is not to say the Mac Pro is unstable or a bad unit but people need to understand that it is not a PC. It is essentially a toaster that you can use right out of the box and pretty much has to stay that way until you get a new toaster.