I think the key is definitely being "fit" more than "not fat"
Everyone knows a girl who never works out, eats junk food all the time, and is still not "fat" - but isn't in shape either. My roommate calls this being a "skinny fat girl." Maybe she's a size 4 but that's more due to being petite and she has no muscle tone at all. When she is in her 40s, she's gonna be screwed!
I was a real gym bunny 2 summers ago - went several days a week, ran, yoga, weight training, etc. LOVED IT. Had so much energy all the time, great muscle tone. Ladies, I HIGHLY recommend weight training - you don't get all bulky (it's nearly impossible without drastic diet changes and mega-intense training), you just end up with nice definition everywhere. Marilyn Monroe used to train with weights and she definitively did NOT look the least bit masculine.
Then I messed up my knees - tendonitis is NOT FUN, people!
Then they got better and I started working out again, yeah!
Then I got in a car wreck. NOT FUN! I killed my poor car. RIP Roxy the Giant red Oldsmobile (1990 Royal Brougham 4 door - the Ruby Limousine!) I also did a number on my neck and back. Good thing I wasn't in a Geo, right?
So anyway, I'm just now in the last couple months being able to get running, etc. again without pain. It just sucks to feel like a little old lady at 23.
The ironic thing is, I actually lost weight from not working out. I stayed the same size but lost all my nice muscle tone.
Since muscle weighs more, without it I weigh less. I'm slowly starting to get some back but it's slow.
I know I'm really lucky though, because I'm tall. Being a size 6 at 5'8" is slender - at 5'2" it can look pudgy on some figures. I can cheat.
Next summer though, when I'm home and have time and money (woo! got a job! yeah!), I'll be back at that gym...just very careful with my knees.
well, the point of this long-rambling-history-of-my-life post was that a girl who is physically fit and has some natural "curves" to her will always look better than the little scrawny girls - the "skinny fat girls."