I'm full time in academia, and specifically in Chemistry.
On a personal level, I do a lot of exam writing on my G5 Quad. The reason for that is that I can't afford a new copy of CS Chem Draw, and the only versions I have are PPC native. I have an SL VM on my laptop, but it's a lot easier to just do the work directly on the G5.
I also sometimes do the same on a G3 Beige "Beast." It's a computer that was given to me, but has a 15K UW SCSI drive and a 1ghz/1mb Sonnet. The person who built it put in a Sonnet USB/FW card along with a Radeon 7000. I upgraded the video card to a Radeon 9200. The computer dual boots Tiger and OS 9, and runs both well, but I primarily use it in OS 9.
I have a spectral data processing program and I can't really find anything comparable-it's quite a powerful program and amazingly compact. It's actually 68K native, and I've run it on my 512Ke from an 800kb floppy. It's primarily run, however, on the aforementioned beige G4.
Although 68K, I often type letters on my 512Ke. It's a nice and distraction free place to work. Both the 512Ke and G4 beige(along with a couple of other computers, including a B&W G3) are connected to my in-office LocalTalk network which has a Laserwriter Select 360 on it. So, I can print from all of these computers on that printer.
Elsewhere in the department, one of our faculty members has a Nuclear Magnetic Resonance spectrometer that requires a PCI PowerMac running OS 9 natively. Actually, we've pushed the boundaries beyond what the manufacturer said and are running it on 9.2.2 but OS X in any for is out of the question.
Also, interestingly enough, we've more or less found the high end of processor speed. I should actually say that it won't run on a 745x processor. After the PSU in the Digital Audio G4 he was using died, I swapped over to a Quicksilver that was in the room. When we did that, we couldn't get it working. The computer would instruct the instrument to send pulses(which we could see on an oscilloscope) and the instrument would output an FID(also seen on the scope). The computer, however, couldn't see it. Installing the 466mhz card from the DA "fixed it"