This MIDI interface not only doesn't work under OS X, it doesn't even get power from the USB bus anymore! How's that for strange? I never knew the power on a USB bus was under software control...
That won't work. My USB Wacom Intuos tablet will not work.

My SCSI devices (ORB drive and Yamaha CDR/RW drive) won't work, because the firmware for my SCSI card is not compatible with OS X.

I have an HP laserjet 5P that won't work (Had it left over from my PC days- connected w/ a USB to parallel converter and works via PowerPrint under OS 9).

So far, all I can do is network my G4 with my G3 powerbook, and exchange files between them. I'd like to be able to use all these peripherals at some point.
All USB Wacom tablets should work just fine with the OS X driver avaialble on their website.

What won't work - my older ADB Wacom Tablet (ArtZ II) with the iMate adapter.

With no driver at all installed, it works as a normal mouse with the pen or puck (no absolute positioning), but I can't seem to get the OS 10.1 Wacom driver to recognize it as a tablet (says there's a "Version Mismatch" between the "CPL" and the driver).

I'm not terribly upset as Wacom doesn't claim support for this device with the new driver, but I was hoping... can anyone give me any suggestions as to how I could get this up and running properly?
I throw my hat in,
Orange Micro SCSI card and all devices hooked up to it: Zip drive, Yamaha CD-RW
My Canon Inkjet printer won't work. Sure, its at the bottom of the current range - I print about 50 pages a year on it, so I just can't be stuffed chasing a solution.
It IS in the current line-up, though.
My macally iShock won't work (cause input sprockets aren't (yet?) included in macosx).

My internal microphone won't work wit classic apps
We can start with the easy:
ProTV card from Formac - no word on drivers
UMAX 6400 FireWire Scanner - working on drivers per tech support
JoyPort USB (PSX, Sega and Genesis to USB adaptor) - no word on drivers
NewerTech U-Drive external USB floppy - no chance for drivers

Things that do not work as well as they should:
iMic (no playthrough from input to output yet)
HP DeskJet 940c (No support for AppleTalk printing yet)
ADB TurboMouse (connected to an iMate) - installed the driver, but the MouseWorks window comes up blank
KeyspanDMR works only some of the time (driver reports conflict and will not respond to input)
Soundsticks sometimes when using iTunes, they will stop producing any sound - switching to iMic and back will sometimes fix this. logging out will also sometimes fix this - annoying either way

Things that work great:
Visor HotSync - restarting classic when it won't sync is better than restarting computer

PS>Wacom tablet works OK.
Canon Multipass C555 Doesnt have any drivers for it and canons being pricks about it
With Mac OS X 10.1.1

Epson Stylus Color 600 USB (Printer)
Sony Spressa USB (CD-RW) [CRX120E]
Microtek Slim Scan C3 USB (Scanner)
Digital DSC Pro USB (Digital Camera)

Rage Pro Open GL Accelerated hardware

In other words, not much DOES work...
My NEC SuperScript 1450N laser printer.

NEC at first claimed no support, but after I badgered them about it, they said a Japanese driver may come out next year.

O goody!!!
My low end Epson printer that I bought after OS X was released (and the reseller told me would work with X) doesn't work with X. My solution? I abandoned Epson in favor of Lexmark. :)
The HP officejet G55 and G85 are also not usable under Mac OS 10 to 10.1.2 over an USB cable! (and i don't have interrest to buy a HP printserver to connect my mac via Ethernet to the printer!) it's all to much money!
Actually if I could SCAN from an ethernet-equipped PSC950, I'd spend the $$$.

I've got a new iMac on order, and since it comes with 10.1 I simply won't be able to use my HP PSC950 AT ALL.

HP, you've GOT to get this fixed!

HP posted the updated driver on 1-4-01. Works great so far.

I'm going to try rebuilding my iMac at 10.1 from scratch -- instead of "upgrade" and see what happens.