Once PS7 and Studio MX were released, OS 9 was an endangered species on my Macs. It's currently residing on my new PBG4/800, but that's only due to my laziness in removing it. I'm waiting for my copy of Jaguar, at which point I will back up all my data, format the drive, install Jaguar, and not give a second thought to not having OS 9 on my HD.
Really, there are a few groups of users who still need 9.
1- Print shops/designers who are forced to use Quark Xpress. Like it or not, even when Xpress6 ships next year with OS X compatability, many print shops will not upgrade. I know of a couple of shops that just recently got Xpress 4.1. This group is slow to upgrade, and sticks with what works for them, regardless of the benefits of hardware/software upgrade. These people will still be using OS 9 10 years from now...
2-ProTools users (and other Midi/Audio apps). While audio apps are starting to migrate to X (Reason, Unity, Peak, Deck are all available) - the big boys are still nowhere to be found. Digidesign says that ProTools will be available for OS X later this year - although they don't say which flavor (LE? Full?). Cubase is rumored to be coming, but who knows when. Logic will be here soon, especially since Apple acquired eMagic 2 months ago.
3-Those who just don't have the cash to sink in to software and hardware for the OS X ugprade.