120 lbs is about right on my 5'5" very small-boned frame. I got up to 131 last summer and had gained it evenly. This is good in a way, except that none of my clothes fit. It was obvious that I was bigger, but I had to work pretty hard to lose the 10 lbs or so.
I range from 122-128 on my 5'6" medium boned frame and feel fine in this range though I prefer when my clothes are looser on me at the 122-125 range vs the 128 range. I can still fit into all my clothes when I fluctuate. So far I can lose a few pounds/gain a few pounds without much trouble and I do so evenly though my chest is the first to gain the weight which you might think is a good thing but I prefer my chest when I am at the lighter end of my weight. I have the classic hourglass figure which I didn't love for most of my twenties (would have preferred to be more flat chested) but have learned to appreciate it as I grew older.
I dont have a small boned frame and have DD cups and a bum ( there's a pic of my *ahem* figure on the bridal dress thread on BWW) These two things never go no matter what I weigh, I lose off my hips and waist.
I look good at 105 but life's too short to diet so much.