My experience is the same. I work in NLP, and I've found that at least everything administered by ACL (probably our largest professional organization) is pretty much always available.
I love that about ACL. Not only is open-access good and nice and all that, but it also means I don't have to screw around with VPNs and such when I need to get an article while I'm at home.
The only thing I do not like about ACL is the fact that is not indexed in DBLP. I have a paper in one of the ACL affiliated conference and it does not show up. I have since then shifted from core NLP and it doesn't really matter but it would be nice to be consistent with other indexing mechanisms.