Personally, if I ever got a message that said something along the lines of, "hey, what's up?", I never responded. It doesn't give much to go off of and you have to consider 10 other guys just sent whatever girl that exact message. I think it's nice to pull something they mentioned in their profile and get them to elaborate or comment on it. It shows you took the time to read it and that you're interested. You have to keep in mind that because there's not physical interaction, you have to work it that much harder in the messages.
Also, work on your own profile. Most guys are terrible at presenting themselves. Talk about the things you love to do and what you're actually looking for from the site.
Agreed. There's something so freaking irritating about the fact that most of the profiles for the guys are all them trying and failing miserably at being witty. I don't care about your love for maple syrup (no, seriously), give me something real to go on. I have been so tempted to message someone with "you ought to re-do your profile because it makes you sound like a total tool when it's obvious you didn't mean for that to be the intended effect" but I haven't, yet.
It also makes me think that most of the people don't even know what the hell they want. I think that's part of my problem on that site, I actually know what I want (stability, someone career-focused, nonsmoker, no kids, not religious) and I think it freaks people out a little.
To the point that another poster made that it's a competition and not a very good place to meet people, I would agree to some extent. I think the percentage of people who actually want to meet someone seriously on these sites is low compared to the people who use it just to stroke their egos.
I'm not sure what to do next though. I checked out match.com thinking that it would at least let you read emails from people before joining, but nope, that site is all about getting your money without letting you even know if it's worth it first. Fuck that noise.
I haven't tried eHarmony but I have a feeling it's probably sort of the same way. I am not quite desperate enough (yet) to actually shell out money to meet the same losers I could meet on one of the free sites.