You can see the ration in the tool tip over the karma.
Interestingly there are users with positive ratios arbitrarily close to 50%.
You can see a comment's karma ratio by hovering on the comment's karma, but to see the user's ratio you need to click through to the user's page and hover over their karma there.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.