A lot of them have seen heavy play. When they first came out, Jace was in a lot of blue-based control decks, but has fallen out of flavor. Liliana is played as a 1-of or 2-of in a lot of decks with black. Chandra used to see play in Limited, but that was about it, she's... not that good. Ajani haven't seen a lot of play either, although before the Kithkin tribe was totally unveiled, I played a White Weenie deck with 2-3 Ajanis, and it was VERY good. Might be good again, now, with the Persist creatures like Kitchen Finks, haven't tested it yet.
I save Garruk for the end, because he's the best Planeswalker, hands down. Sees HEAVY play. Just check some decks, basically ANY aggro deck packing green packed Garruk a while back. He has been cut from some decks to make room for the aforementioned persist critters, but he's still VERY good.