I get annoyed with crossposting usually, if it's more than 3 or so places - but not so annoyed that I feel the urge to scream about it. I think one's lj (if one wants to go there), a general fic comm, and a character or pairing-specific comm is a plenty. Like, if I wrote some Harry/Ron pr0n, I'd post it to my fic lj, pornish_pixies, and harry_and_ron. If I wrote Sirius/Lily smut, it'd be my fic lj, erotic_elves, and siriusxlily. If it's not smut, I send it to FA instead of PP/EE. That's just my preference though.