I can speak from my experience having released an MMO strategy game that runs on iOS, Android, webOS and most web browsers (http://spaceuncharted.com). JQM is far from perfect, but its compatibility has been solid. It was really nice to be able to write the app once, and use Phonegap to have it run on all the phone platforms with only minor tweaks. I originally wrote the game using the WebOS SDK in Javascript, and porting to PhoneGap seemed to be a reasonable thing to do...
On performance, we've found that on older devices, changing pages can be pretty slow, but on more recent hardware it's quite usable. Scrolling hasn't really been a problem except on fairly old hardware, such as the original Pre and some older Android phones.
We did run into one odd problem when overlaying some jQuery Mobile buttons over the HTML5 game canvas because the buttons used css border-radius, which reduced framerates by about half. We were able to switch to custom buttons that used css border-image instead, which had a much smaller impact on the canvas performance. But that really seems to be a bug in the mobile browsers rather than a jQuery Mobile issue.
On performance, we've found that on older devices, changing pages can be pretty slow, but on more recent hardware it's quite usable. Scrolling hasn't really been a problem except on fairly old hardware, such as the original Pre and some older Android phones.
We did run into one odd problem when overlaying some jQuery Mobile buttons over the HTML5 game canvas because the buttons used css border-radius, which reduced framerates by about half. We were able to switch to custom buttons that used css border-image instead, which had a much smaller impact on the canvas performance. But that really seems to be a bug in the mobile browsers rather than a jQuery Mobile issue.