I own J. Lo - Glow - which is clean, soapy, with a bit of musk. I like it. It's easy to wear and light. Doesn't last too long, but actually lasts longer than some "name brand" fragrances (Burberry comes to mind). I also own Britney Spears - Fantasy - which is cotton candy sweet and (on me) sometimes dries down to a nice vanilla/tobacco/musk scent. Sometimes. I've smelled Love at First Glow - light, sweet fruity floral, very inoffensive, and Lovely - clean musk scent.
Oh yeah, I also smelled Paris Hilton - Paris Hilton - which was compared to Ralph by Ralph Lauren and I find them pretty similar with Paris being longer lasting because it's an EDP.
So far the ones I've smelled have actually been pretty good. But you have to remember that it's not the celebrities *themselves* coming up with the fragrances. There are real perfumers coming up with them, they just use the celebrity name to sell it.