I stumbled on Portofino in much the same way while browsing the web. We will be visiting Belize for the first time in April and will be staying at Portofino. We went for the honeymoon package in the Royal Orchid suite, which looks fantastic on the website. The package includes snorkeling trips and a "try-dive", and other goodies like champagne and wine.
While snooping around this (very informative) message board, I learned that the major drawbacks of Portofino are the absence of a pool and access to town. But I think the beauty and peace and quiet of the resort will make up for all that.
If you do decide to stay at Portofino in March, let me know how you like it.