Google have announced that site links will now appear for mobile-targeted Adwords ads:
This will currently only work for 2-line site links (probably due to the lack of width on some mobile browsers) and only 2 links will be shown at a time.
Placement ads will be able to show site links wherever they appear (above or below the fold) and Google is pushing the double-whammy effect of using both site links and click to call phone extensions on mobile campaigns.
Site links are good for mobiles as users may want to click straight through to a deep linked page – especially where they want information fast on their mobiles and on the go. Been asking for this one for a while!
More info in Adwords Help Centre.
A key item to remember is that you may be using trademark symbols (™) in your desktop ads and site links. You can use trademark symbols in mobile text ads too but not in mobile site links because they do not display correctly:
e.g. Hoover(tm) Dishwasher
instead of Hoover™ Dishwasher