I don't have a Mac, but three of my coworkers (out of a team of six) use Macs for Java/webapps programming (that's cross platform anyway). My wife does bioscience research in Berkeley and they use a mixture of Macs and wintels.
I think just about any job you can think of, you can use a Mac (more or less). In some jobs it might not be a good idea (think: Windows Developer), and in some jobs it's a match made in heaven (think: Graphic Design).
As a graphic designer I use a Mac everyday at work.
As for other professions I remember reading on the Apple site that the last two US Presidents both used Macs, so that's another job to add to your list. 😉
And lets not forget the all important "Steve" jobs. Hahahahahahhaaaa. I crack myself up. 😀
I think generally speaking you can do pretty much any job with a Mac. Wether the company you would be working for would let you might be a problem, though. You'd be surprised at the Mac ignorance still out there. "Macs wont work on a windows network", etc.
How many people have worked somewhere that has a proprietary database set up on Macs? For example, a grants-management database writen specifically for a particular grant-giving organization. These sorts of things, without really knowing, seem to me to be one major obstacle for a lot of companies adopting Macs. Corporate accounting software?
The places I've worked that use macs tended to be in publishing or advertising, and data tended to just be kept in excel spreadsheets.
Access is missing for macs. It would be awful nice if Microsoft would port it.