Yes, that's exactly it! I had figured out the social expectations on lj -- and I did lock, for discussions of work/school/things involving the word "megaupload" -- but now the tools are different AND my content is likely to be different, so it's hard for me to figure it out without trial and error.

Also, you make a really good point about the way granting-access may make folks feel more welcome to comment even though there's nothing locked.