I really miss the possibility to send a personal thank you message to people that helped me. I've just read some topics in this meta about this. According to a moderator:
"Just say thanks and add something like \${}{}{}{}{}\$ which is invisible and takes up space."
Some people argue that short messages like "thank you" are just noise, and should be avoided. Others think that 'thank you's' should only be posted if you explain why you're thankful, why a post was useful to you.
My personal opinion is that it is just a healthy human desire to express gratefulness. But I also agree that for it add noise for all the other readers. I could say thank you and put some more details why the post was helpful, but most of the time I'm thankful not in any rational way. It's just an emotion that I want to express when someone spend time helping me out.
What about being able to leave a personal message on a profile ? This keeps the noise out of the topic without holding back normal human interaction.