Does anyone know what the points associated with achievements signify? I am talking about the values of 5, 10, 15 and 50 that appear on the Achievements tab in the Journal. Do they serve a purpose besides indicating the relative difficulty or time necessary to complete the achievement?

I think you're exactly right. They probably indicate how hard or time consuming an achievement is.

I am wondering where can post our achievements? They are not that much fun if they are easy to share. I really like them auto show up on the ESO forums so I can compare what I have down to others. They are a fun mini-game, kinda sad if one have to play it solo

...would be a neat feature to see in a new forum and after release. But yeah, most likely difficulty...unless they have a plan for giving skill points every so many achievement points or something, but who knows.