The Yikes! was one of the last G4 towers I needed to complete my collection. It actually proved fairly difficult to find(then I bought another locally a month later, as it seems things often happen with PPC Macs).
These are interesting towers. If you look at the logic board, you'll actually see solder pads for the ADB port that was present on the B&W G3 but deleted from the Yikes!.
I have a 1ghz Sonnet G4 in a G3 beige minitower, although the processors are pretty freely interchangeable across the the three different ZIF logic boards(with the exception that B&Ws need to be "unlocked" for G4 support).
The one caveat to the 1ghz Sonnet is that it requires you to lower the bus speed to 66mhz. For that reason(among others) I've elected to leave it in the beige since that's their default bus speed and thus one of the few advantages of using a B&W or Yikes! is that you can shove in an extra 256mb of RAM.
There's also a very scarce 1.1ghz G3 upgrade. This particular processor has an extremely low TDP and can actually use the stock heatsink in a B&W or beige G3(the Yikes! heatsink is huge compared to the two). By contrast, the 1ghz Sonnet G4 uses a heatsink about 2 1/2 times the length of the ZIF socket and with two fans on top of it.