Watched it tonight, and it was pretty good. The film is based on The Sands of Time storyline, involving a mystical dagger than can rewind time. The effect is used sparingly, but is impressive enough and despite my early misgivings Jake Gylenhaal was spot on too, he looked the part and his British accent was very consistent and oddly in keeping. I'm not a huge fan of Gemma Arterton's, she's attractive enough, but lacks the charisma to carry off a leading lady role; luckily, Gylenhaal carries that part fairly well, and they're both helped by the script, which is fast paced and just witty enough.
Suffice to say, the ending is a touch predictable but it's executed well. I won't go into it here for fear of spoiling it. Good cast too, including Ben Kingsley and Alfred Molina.