Maybe it's just me, but from time to time I try latest Servo build and it never survives more than few minutes of usage before crashing. Last time I did it was 3 days ago, I opened a website and it crashed with "RefCell already borrowed" in what seems to be a logger module. This always strikes me as weird because one of the selling points for Rust is memory and thread safety (quote from the website: "eliminate many classes of bugs at compile-time").
Yes it's safe but undesirable, like Java's NullPointerException.
A more interesting question is why it was not possible to use compile time borrow checking in this particular case. It shows how valuable the borrow checker is when you can use it.
