That's what got me into trouble with my Chuck fic and how my 4,000 word story turned into a 30,000 word story. I let the readers decide.
This is the first time I've done that. My stories have no problem becoming long, because I usually let the characters decide what they should do. (I know, stupid, right? /shakes head/ They *never* want their story to end. They're always rambling on in their minds about this and that or whatnot.) It's why my 11th file of Wrong Clark (do you really even want to know this?), which only covers parts 184-206 (roughly) is 95K words and will probably be over 100K before I start my 12th file.

(300-350 pages of double spaced story per file is long enough, don't you think?)

Nah. You didn't want to know that. Congratulations on getting to 30K.

Once you get that far in, it's the stopping that gets hard. By then, it's become an addiction. You love these characters and you don't want to leave them to go work on something else. I completely understand. Hmmmm. /Considers new self-help group: Over-Writers Anonymous. /