Yesterday I reviewed a book for PW featuring a heroine who was both a Poor Little Rich Girl and an Ugly Duckling. I've not been a fan of this combination since attempting to read Judith McNaught's Paradise years ago. Either one of these premises alone may or may not work, but as far as contemporaries go, the combination adds up to something reeking of whatever is the opposite of a "modern sensibility."
I've got less of an issue with the Ugly Duckling premise, which I imagine works for any woman who isn't drop-dead gorgeous, but in general the Poor Little Rich Girl is only palatable for me in historicals, where "old-fashioned-ness" can be kind of the point...and a good half of heroines are wealthy and titled. (I guess you could contrast Paradise with A Kingdom of Dreams, my favorite McNaught book, and right at the top of my list of favorite Medievals.) But back to the Poor Little Rich Girl. It's one thing for a heroine to feel like a ghost in the world if she was raised by parents who ignored her - which can happen at any income level - but by the time you pile money on top of that, too often you end up with a heroine who needs therapy more than she needs a man.
I'd be interested in your least favorite premises...or least favorite combinations.