Unlike mobile (i.e. smartphone and featurephone) searchers, tablet searchers are not focused on completing a task (Mission), but are instead using the search engines on their devices to find new and interesting content, without really knowing what they are looking to find (Exploration). And neither tablet nor mobile searchers are using their devices for multi-step problem solving (Excavation).
If you’re lumping tablets and smartphones in the same ad group, or serving content created for mobile users to tablet users, you could be serving your customers content they don’t want.
Bryson Meunier, What You Need To Know About Targeting iPad & Tablet Searchers, Jan 30, 2012
Very interesting findings on how tablet users’ search and content consumption differs from usage on desktop and smartphone.