Based on what dragonworks wrote on this thread: Of course Britney Spears' voice is very good...when recording in the most advanced studios in the world, most voices will sound very good. A little (or alot) of pitch shift here , oops...over there too, oh! How 'bout back here.
In live performances though, it seems like she lip sychs the songs she sings 'cause, when she sings/dance, she never looses her breath & is always in tune.
I read some portions of her bio from several websites. It appears that she didn't write any of the first album songs. A guy by the name of Max Martin (or someone from Ace of Bass fame) had much to do with getting her singing career going. I believe that she wrote a couple of songs for the current album release.
So don't blame her for writing lousy lines to the songs that she sings. She's just a "circus act"...part of the pop machine team. The people behind her scene are running the show and to the bank while they maintain their own privacy. Spears has lost her privacy while all she has to do is sing in the studio and, correct me if I'm wrong, lip sych and exercise on stage. I'd hate to be in her shoes and lose my privacy.