Annotatr looks somewhat similar yes. They too have some issues with getting to critical mass, but you have to start somewhere. I have to look into integrating more services into Tiris (pubget, citeulike, mendeley). I think the biggest difference will be when I implement the embeddable commenting system, which should enable easier access to Tiris.
About dropping me a note, hmm, yeah, that could be a bit difficult. Sorry about that. If you come to my site http://www.juretriglav.si - there is an email link right at the bottom of that page. Sorry I have no better way.
Off-topic: How does HN usually solve this lack of PM issue?
Many people put their email in the About field of their profile. You can obfuscate it if you wish, or just trust your spam filters.
Take a look at this project which is similar to yours (not mine btw): http://annotatr.appspot.com/