One of the things that always gets my gander up when I get comps and mockups back from designers is when there are buttons in places that links should be. For whatever reason many designers/UI people really like buttons and put them all over the place. There are pretty defined guidelines for when to use buttons and when to use links and these are often not followed.
Why “Cancel” should be a link, and not a button, by Karim Maassen
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Why “Cancel” should be a link, and not a button, by Karim Maassen