What are the 8 devices?
I'm guessing
Keyboard
Mouse
Printer
Scanner
iPod
Digital Camera
PDA/Phone
Media card reader
possibly replace any one of the above with an external Hard Drive...
Am I close?
On a Mac the mouse and keyboard only take up one USB slot since the keyboard has another USB slot for your mouse... or even better yet, you can go wireless for those with the built in bluetooth...
You can pick up an Airport Express to take care of the printer and now you have a network printer available to all your computers...
Depending on your iPod generation you might be able to sync/charge via Firewire, or if you have an external HD you can upgrade to a firewire enclosure for around $30, maybe less now, I haven't looked in awhile.
That should be enough to get the 8 into 5 (even have one left over if you can get a wireless KB and mouse, and upgrade at least one peripheral to FireWire).
If we knew the types of peripherals and aesthetics are more important than cost I'm sure we could come up with a solution to free up USB ports on your iMac and possibly even enhance your setup at the same time...
would splitting a usb via a hub slow down the transfer speeds?
No, it won't.
Rich
To be fair this may not be true. If you plug in a bunch of hard drives to a single hub and then try to do large file copies to all the HDs simultaneously, then, yes, you will see a throughput drop. But the vast majority of USB devices (printers, keyboards, mice, digital cameras, etc) are either low data rate or only brief periods of high data rates combined with long downtimes. These will not show a significant drop in throughput on a hub since it is unlikely that they will all be doing large simultaneous transfers.