I tried AppMobi early on but as a developer I much prefer something open like PhoneGap, even if (or because) I have to glue the pieces together by myself. I don't really see the demographic that knows how to develop an HTML5 web application but prefers a closed black-box environment for putting together the mobile app.
The AppMobi XDK was pretty slick though. But from the announcement it seems like they pretty much tore it down and started over from scratch.
These days I hold higher hopes for real convert-to-native tools, that actually translates HTML5 (f.ex. the canvas API) to native code.