One of my friends from Birmingham has this name. It suits her and I sometimes like it and sometimes don't. I hate it as a man's name, to even think of it as a man's name, eurrgh, our world is a strange place.
I'm not a fan of Hillary Duff, so I don't really like this name. She is the first person I think of when I hear this name, and I do not want my daughter to think, "Hey, she's got the same name as me, she's gotta be my role model." Un-uh. Every Hillary I seem to come across is wild and mean and has no morals to speak of what-so-ever. I wouldn't name my daughter Hillary any-thing, but as for a middle name, I guess it might be okay. But still, it's a NO WAY in my book.
I like this name very much. Not only does it mean "cheerful", but it has a pleasing sound that is neither too feminine nor too butch. I prefer the double-L version myself.