Well, I think it's fine, and even admirable, to tell people about it, especially if you're 'seriously' dating and looking for a long-term partner rather than just 'casual' dating.
Here's a cautionary example of how not to bring it up. When I was dating (online) I was chatting with a fellow and he seemed nice so I asked if he wanted to meet for coffee. He said "I can't have coffee". I said, "how about tea?" He got a bit snappy, and said that he'd had bypass surgery and couldn't have hot beverages or carbonated beverages. After that I just did the fade away. I didn't give a fig that he'd had WLS, but it really bothered me that he seemed so put out by a normal suggestion and unable to adapt to his own circumstances. He didn't even suggest an alternative. Meeting for coffee is a normal thing, but if you can't have coffee for whatever reason, just don't order the coffee! I wouldn't have even noticed if he sat there sipping Water.
If someone invites you to a hot-dog eating contest, of course you're not going to eat 27 hot-dogs, but you can still offer to do something else. food and drink are social lubricants - especially when you're dating. Being up-front and positive about what a great thing WLS has been for you rather than a downer about the stuff you can no longer do is the way to go. Someone who's terrified to date you because you used to be fat, is not someone who's going be supportive long-term.