I've used Zoetrope's virtual studio to get short story crits, and it was good for that, but I've only used it on one story so far because most of what I write is longer-format.
I also belong to several Yahoo groups for writers, one connected to a workshop I did years ago, two regionally-defined groups (neither of which is at all active) and another fantasy writers' group which was great in the past but isn't as active as it used to be.