Matthew Gilbert at Boston.com says Palin was "playful," and the clip he provides makes the point.
Here Politico compares (with clips) Palin on Leno with Romney on Letterman (who appeared with Letterman last night), calling the counter-programming an "epic battle of late-night hosts and prospective 2012 Republican presidential candidates."
Also with clips, Mark Memmott at NPR says both Palin and Romney "got in some good lines."
Who won the ratings battle? At TV by the Numbers, the headline over Robert Seidman's report declares, "Leno Crushes Letterman in Return."