I like how easy it is to get Zepto up and running. It's a great library for building small applications. I can't say I have any downsides. I'm using it to build a simple application that will help us maintain/create a list of our website's pages. The application will be used by our website's editors to update the site's pages. We had some issues when we first started using it, but we were able to resolve them quickly. In a few weeks, we had a functioning application, and we've since been able to build out the rest of the application.