I have a web application I am building (nvrforget.com) that has a launchrock splash page and I considered emailing each individual sign up to find out what they need help with related to memorizing, but I decided that it was bordering on creepy so I didn't. Is this true? or is that a good idea?
I don't think it's creepy, as long as you don't bring up information that might be too personal.
A rule of thumb I read was "Would this be creepy if it happened in real life?", and here you'd be analogous to "a restaurant owner asking a customer how their experience is on their opening day", which is totally normal.
I used to send a quick one liner saying I'm rob, thanks for signing up and let me know if there's anything I can help with.
It led to a lot of useful conversations. We already had a running service at the time though, so not 100% sure it transfers to a pure landing page.