My husband didn't want our kiddo to start kindergarten early because when he was in school, he was the youngest and smallest and it was harder for him in sports (he still excelled). However, after having him tested and seeing that our kiddo is not sporty, DH changed his tune. DS8 is effectively skipped 2 grades (one grade skip, one transfer to an accelerated school), and it's been a great fit. He is on the smaller side, but there are other kids his size too (some are also grade skippers, and some are just small). My DH also mentioned that he didn't really have a growth spurt until after high school, so if my DS is like dad, it wouldn't matter if he skipped or not; he'll just be a late bloomer.
Some of the things we considered before the skipping: sports (not really an issue for our nonsporty kid), academic competitions (DS will be younger than the kids he's competing with -so far not an issue). The main thing we considered was that we needed to give our kid the same chance to learn new materials as other kids, so that he is not shocked when he gets to college and meets his first challenge.
I can tell you exactly what I thought when all my friends were driving and I wasn't yet, as I was the youngest in my grade: this is awesome, now I have friends to drive me around. Although I wasn't grade skipped, my boyfriends were all older than me by 1 to 3 years, because those were the people I got along with.
We are happy that we didn't have to skip our son more, since there was an accelerated program relatively near, but we were prepared to skip again in our local schools if necessary.
