I used JQuery Mobile for the mobile version of our site. Performance is definitely an issue. I believe that it will eventually improve with future versions so I stuck with it and used just a subset of the features that had acceptable performance. The compromise in performance was worth not having to worry about cross-device compatibility.

Specific performance issues I ran into: 1) The page transitions were too slow so I didn't use them at all and instead just do page reloads for everything. https://github.com/jquery/jquery-mobile/issues/3217

2) The list structure causes scrolling to be too slow so I had to switch to generating the CSS classes and html structures on the server: https://github.com/jquery/jquery-mobile/issues/2855