Forum Moderators: open
I simply don't have room on the desk for a mouse. (The trackball sits on my lap).
Don't know about Illustrator, but I can do everthing I need with a trackball.
You do need to keep them cleaner than a mouse -- daily gunge build-up can make them awkward to move as the friction licks in....Remember, your greasy thumb is in direct contact with the moving part.
I had to change brand recently -- owning to the old trackball dying. Took me about 3 days to get used to the new one (there is less of a standard layout for buttons with a trackball).
In my experience, it takes about 2 weeks for full mouse-to-trackball switch or vice versa. You can get relatively comfortable in a few hours, but the precision dexterity takes a while. Once your muscles learn what to do, though, you'll be fine. You stop having to *think* about what you're doing in a pretty short amount of time.
And for me, it's worth it. Better control, less movement of my hand/wrist, and comfort.