Laura Prepon

One thing seems fairly certain — she's not the mother. Still, Laura Prepon is poised to have a very good time guest-starring on CBS' How I Met Your Mother later this season.

That gal from That '70s Show (as well as October Road) has been cast in the role of Karen, a rather infamous ex of Ted's. Yeah, it seems these two have been off and on and off again countless times since college - to the point that Lily visibly seethes at the mere mention of repeat-cheater Karen's name.

Now, why do I dare venture that Karen isn't the mother? Well, 1) the show isn't called I Had Already Met Your Mother, and 2) Prepon is only around for two episodes, not five as reported elsewhere.

But I like this casting, especially given the somewhat naughty nature of Prepon's role. Are you willing to let her break Ted's heart one more time?