Disclosure: I'm a contributor to jqm. The most important differences I see in the mobile frameworks available now: 1. As mentioned in one of the other comment

Disclosure: I'm a contributor to jqm. The most important differences I see in the mobile frameworks available now: 1. As mentioned in one of the other comments the device support is much more comprehensive. Symbian and BB 5 devices are being sold in large quantities every day and the project's goal to support them is an important one. 2. Jqm uses augmented semantic markup for layout, whereas sencha (afaik) uses templates from within Javascript. 3. The jquery community produces a lot of interest, a lot of contributions, and is generally very vibrant. I'm spending most of my time trying to keep up with the pull request back log (apologies to all those still waiting) which is an enormous asset to any oss project. Hope that helps answer your question.