The first person to mention it was a Tweeter (don't know who exactly, I found the tweet on the Pottershots forum):
lmao my mum went to a yoga retreat with emma watson
Then, today, hrrybb wrote on Tumblr:
so today my grandma told me that her best friend recently went to a yoga retreat in the rocky mountains, and they had to take a vow of silence for the duration of the stay. when she entered the retreat though, she recognized this young girl and spent the entire week not focusing on yoga but trying to decide if it was the the girl who played hermione in harry potter. on the last night they were able to break the silence and have a group dinner, and it ended up being the real emma watson. i guess she wants to teach yoga or something.