Our Panama Canal cruise (RCL) had a small outbreak and they basically shut down the "self-serve" buffet and had all dining staff on hand to serve people. We, ourselves, never got sick. That is the only time we saw a problem.
On Celebrity, we were not allowed to serve ourselves at the buffet anyway - they always had serving staff.
I think the "open-buffets" are probably a large contributor to the problem. Many people try to avoid them by eating dining room only. But I have heard of some of these people getting sick also. Using a handrail, etc. is an easy way to pick something up. From what I understand, if you go to the infirmary, they will quarantine you. A lot of people choose to just take care of themselves, so they avoid the quarantine - which may just make the problem worse - depending on how much they are taking care of themselves.
You definitely want to keep washing your hands, using the Purell (bring your own also) and always check your glasses, silverware, and dishes before you eat. More than once I found a coffee cup with lipstick on it. We reported it, only to find another one the next day.
All in all, it would not stop me from cruising.