Ah, ratings. This is one of my bug-bears as there really doesn't seem to be any kind of definitive 'rule' when it comes to what warrants what rating. I have read stories rated G that I would rate R; equally I have read stories rated NC-17 that I would rate G - and I think I over-rate. As such, I pay little attention to ratings when I'm reading.
When it comes to rating my own stories, I don't rate on my own website. However, I do make a point of telling people I don't rate and why I don't rate. And I do an 'overall rating' on the main page for each fandom, so people know stories on that part are rated between G and R or whatever they are. When posting to LJ communities, I rated, because it was expected.
I also for the most part only rated for sex; I didn't rate for language (not that I used a lot of bad language) or violence (again not that I wrote a lot of violence) or anything else. My ratings were pretty much only intimacy/sex based.
Oh and I rated exactly the same for het as I did for slash. I have come across a het stories rated PG and slash stories rated NC-17 where the amount of sex/intimacy, etc. is exactly the same, but because one is slash the author thinks it should be rated a lot higher.
My personal way of rating was/is:
G - The couple in the story are only mentioned as a couple.
PG - The couple kiss in the story.
PG-13 - The couple going to bed together is mentioned in the story.
R - There is some description of sex.
NC-17 - There is a reasonable amount of sex described.
As for what I'm comfortable with, I have written stories ranging from G to NC-17. That said, from what I have read I suspect my NC-17 stories in particular are over-rated. I'm not overly comfortable with writing lots and lots of detailed sex, but I have done it if the story needs it. I'm probably most comfortable around PG-13 (well my version of it).
I'm somewhat bemused by the idea that someone would be 'shocked to discover a story they had written was G-rated'. Surprised, maybe, but shocked? Why would someone be 'shocked'? I can understand someone being 'shocked' to discover they have written NC-17, when they are really only comfortable with writing G. However, I really can't get my head around my someone who is comfortable writing NC-17 would be shocked to discover the story was 'only' G.
That said (getting back to answering the question) no, I can't say I have ever been 'shocked' by 'discovering' (although why I would 'discover' it, given I'm writing it, I know not) a story was a particular rating.
14 – Ratings – how high are you comfortable with going? Have you ever written higher? If you're comfortable with NC-17, have you ever been shocked by finding that the story you're writing is G-rated instead?
15 – Warnings – What do you feel it most important to warn for, and what's the strangest thing you've warned for in a fic?
16 – Summaries – Do you like them or hate them? How do you come up with them, if you use them?
17 – Titles – Are they the bane of your existence, or the easiest part of the fic? Also, if you do chaptered fic, do you give each chapter a title, or not?
18 – Where do you get the most inspiration for your fics (aka 'bunnies') from?
19 – When you have bunnies, do you sit down and start writing right away, or do you write down the idea for further use?
20 – Do you ever get bunnied from other people's stories or art in the same fandom?
21 – Sequels – Have you ever written a sequel to a fic you wrote, and if so, why, and if not, how do you feel about sequels?
22 – Have you ever participated in a fest or a Big Bang? If so, write about your favourite experience in relation to one. If not, are there any you've thought about doing? And if not, why not?
23 – When you post, where do you post to? Just your journal? Just an archive? Your own personal site?
24 – Betaing – How many betas do you like to use to make sure there aren't any major flaws in your fic? Do you have a beta horror story or dream story?
25 – Music – Do you listen to music while you write? Do you make playlists to get into a certain 'mood' to write your fic? Do you need noise in general? Or do you need it completely quiet?
26 – What is the oddest (or funniest) thing you've had to research for a fic?
27 – Where is your favourite place to write, and do you write by hand or on the computer?
28 – Have you ever collaborated with anyone else, whether writing together, or having an artist work on a piece about your fic?
29 – What is your current project or projects?
30 – Do you have a favourite fic you've written? What makes it your favourite? And don't forget to give us a link!