Garry Newman of Facepunch Studios, developer of Rust, reported on Twitter today that the 329,970 copies of the Early Access survival game have been refunded on Steam. According to Newman (in another tweet), that comes to around 6% of all copies sold. (Extrapolating from that, it appears Steamspy's estimation of 5,509,983 Rust owners is pretty close to the mark.) In terms of dollars, those refunds total an eyebrow raising $4.3 million USD.
It's probably not quite sensible to look at the $4.3 million as a straight-up loss of revenue. Since Steam began allowing refunds of games played for fewer than two hours, customers have presumably become much more cavalier about purchasing and trying games, knowing there's a safety net if they decide they don't want to keep them.
I asked Newman via Twitter what the most common reason given for requesting a refund was, and he replied "Not fun followed by bad performance - which is pretty fair I think."