I think het (or femslash) does tend to feel a little to home because we have girl parts ::g:: I can imagine what it feels to have your cock sucked, but I'm never really going to be able to experience what it feels like (without a lot of surgery and even then...)

But with het or femslash, we usually have experienced some of the things that the characters are experiencing - we generally know what it feels like to be penetrated or have someone go down on you, at least from a woman's perspective, and so there's that lack of distance. There's always that wonder whether people reading it are going to assume that these are your reactions rather than the characters. There's always that wonder whether you really are projecting.

Which is weird when you think about it, because you don't generally feel that way when you're writing two men getting hot and sweaty together. But then it's more firmly in the realm of reality.