To answer your question, "it depends".
First let me say that I love OS X. I actually miss it when I am working in 9 at my work (prepress graphic arts house). But there is still a few problems that need ironing (most of which will be fixed in 10.1). OS X is the most beautiful computer OS that I have ever seen. As a graphic artist, you are going LOVE the looks of OS X. I love the fact that almost everything is anti-alised.
Photoshop is about the same speed in both 9 and X, although I have not performed a real time benchmark... just my opinion. The only problem that I have in Photoshop is that sometimes when I start it up, the menu bar is missing. No problem, just quit and start it up again and all is fine with the world.
I have not worked in Illustrator in X yet because I am more of a Freehand person.
I haven't noticed any problems in Quark yet, except it sees every file on your hard drive (including the invisible files and folders, but it has always done that...), so it is a little more confusing to navigate when you are saving files.
I am not sure if there is a Carbon version of Flash yet, but if not it should come out soon. Maybe as a downloadable update.
The problems with OS X and graphic design are:
1) I find sharing files between computers more difficult. I still have not been able to get Appleshare to work like normal. To access my OS X mac, I have to type in the IP address instead.
2) Printers are having a hard time with support. Especially if you have special drivers like imagesetters.
3) Some programs may not work. Technically, 90% of all Mac programs (going all the way back to OS 7) should work in OS X. If you have special prepress or postscript software, it may not work for you.
4) Adobe does not plan to release a font management tool (ATM) but I am sure someone else will. Right now, you just have to do it the old fashioned way. I have had problems with fonts displaying incorrectly in Classic applications too, but not in any of the Adobe products.
All in all, try it out. Work in it for a few days to see what you think, it cannot hurt. But, if you are in a crunch to get your job done, stay with 9 until you have more time.
OS X is definitely worth the time.