I just received my SonnetCrescendo/WSin the mail today. It is a 500 MHz CPU upgrade for Wallstreet PowerBooks (which have 233 to 300 MHz originally).
I installed mine into a 300 MHz model: Before installing the new CPU, whichis as easy as swapping a memory card, one needs to run a application fromthe supplied CD. This apparently prepares the upgrade (performs a ROM copy,perhaps?) but does not appear to add any new extensions to the Systemsoftware as far as Conflict Catcher can tell. I also own a 500 MHz iBook Dual USB and I did some speed comparisons, which turned out to be very surprising.