A little late to the party but I'm developing a project with a designer who is absolutely in love with modals.
For mobile devices in 2014, modals are still a poor UX choice because of positioning and scrolling issues.
From a feature perspective they sure do look slick! For me, however, that's just about where their allure ends.
A UX focused approach is to consider that all modals have a trigger element, something important or compelling you want visitors to click on which will reveal your modal and its information. The modal contents also must therefore be important (otherwise you can eliminate the modal, right?) but they are in some form of UX limbo because the modal content isn't important enough to deserve its own page... but the content is important enough to jank up a visitor's mobile experience. So which is it?
If you're designing and developing mobile first (which you should be these days), then modals can probably be replaced by a more tried and true methodology.
Even a small modal may require a mobile user to scroll through the modal content and reveal the modal's UX shortcomings. If your content is short and doesn't require scrolling then use one if you must. If your content requires scrolling then consider trimming your content, giving the content its own page, or going with a more tried and true UX.