I think I’d spin this question around and ask you to think about the kind of problems you have today in your site. If a HTML5 feature can help you solve one of those problems then great, but I wouldn’t go searching for features and then try retrofitting those features to your site just for the sake of it.

You can use sites like caniuse.com to give you an idea of how good browser support is for a particular HTML5 feature. However, even if a feature isn’t supported there is a good chance that a JavaScript Polyfil is available to enable you to use a feature and have it gracefully degrade in older browsers. Last week I should a good example of this with HTML5 Form validation.