Hi there,
If you feel that people's interest isn't translating into sign-ups, maybe there's just a disconnect between the game and the website calendar. Have you considered using the in-game calendar to set things up? Maybe it would provide a more accessible reminder of upcoming awesomeness. Then again, maybe "accessible reminder" is just a nice way of saying "beating-everyone-over-the-head!" :-) I get the impression that, in the past, the sign-up mechanism was certainly no barrier to getting regular raids going, so who knows.
As for myself, I'm pretty easy to please - any kind of group content is good fun to me... 5-mans, raids new and old. I should be pretty consistently available for the Thursday night slot, and could probably make a second night during the week as long as it's not Wednesday. Sunday night is another possibility.
Meanwhile, the "summer slow time" is almost over, so things may pick up on their own soon.