Everything I write has at least a small part of myself in it, be it fanfic or realfic. In my AFF originals, the story of Tanya (that's her real name) appears in a few different places as background for what my characters do. Many of my other stories draw their main characters' characterizations from people I know in real life -- in my Marianne stories, for example, Michael and Rebecca are two people I know from high school, though I have no idea what either is doing right now, as I haven't talked to them in ages, and can't find them on MySpace.
As for personal experiences, I, like Jadwin, like to include little bits of reality, though I don't necessarily go out of my way to find out if something is true. Like, for example, in one thing I'm writing, I made up a bar/restaurant (think Chili's but with more American food) in Norfolk, Virginia, where they always show Miami Dolphins games. I'm sure such a bar exists, but I've never been to Norfolk, so I can't be certain. However, the bar is based on a real one I've been to in Florida.
I think the best stories incorporate reality and unreality -- the devil is in the details, whether it's a character tossing her lunch trash into a brown plastic Publix bag or doing something as simple as mentioning a seemingly-useless detail in passing. In reality, we notice the tiniest details most when we're focusing on something else. At least, I think so.