So, you have to reply to someone's tweet to add it to a collection? That seems... less than ideal. Did I miss something?
Yes but the reply Tweet doesn't have to be limited to the HashFav tag; it can be embedded in the reply similar to the hashtag (e.g. "wow, this is ##cool"). Replying to the Tweet also serves to notify the author. However if you want to be stealth, you can copy-paste the URL to add a Tweet into a collection.
You might be interested in http://www.tweetd.com/. It extracts links you tweeted and presents them in a easy to use style.