does reinstalling OS X using recovery erase my data?

This worked like magic!!!

I was able to execute the remove command using one Mac (the one that would start but not log in) by restarting in single user mode and them mounting the hard drive in read write mode.

/sbin/mount -uw /

No, but make a backup before starting, and set some time aside to let it do its thing. It took me two hours on my iMac 27" the other day.