Are you pregnant? If so, then you should limit yourself to one serving per week. If not, then go nuts! I like tuna, but I can only tolerate it a couple of times per week, so I'm certainly not worried about getting poisoned by mercury.
i do eat quite a bit, about 3-4 cans a day. I only do because its cheap protein and fast meals to prepare. Rest of protien is chicken and beef. That site recommends not eating more then 3 cans a week for my weight.