I have no option to leave a comments either. (I've noticed thou that I have option to comment on my own posts / answers, but I didn't try them out.)

After I post an answer there is an option to "Convert as a comment". But if I click it, the answer simply disapears (I tried twice in two different ocasions and it hapened in both cases)... Funny thing also, is that there is an option after Fabien's comment that sugests me to convert he's comment as an answer. Maybe that's all a problem with permissions.

I also noticed that there is no longer un option to insert preformated code in our questions / answers...

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EDIT:
I edited my anser because I tried to comment my own question to confirm that "new feature" stated on Roel's answer (Closed questions returns a "Internal Server Error" message)... And I guess comments are not working because nothing showed up after I click "Post".

Doesn't work for me either.
Tried it from my ipad and currently firefox under windows. (Fonts under firefox windows are ugly by the way)
Comment vanishes and is gone forever, no errors.

When I try to change my profile or view closed questions at least that gives me an 500 internal server error..

Edit: Woops. Managed to delete Fabian's answer by clicking Convert to an answer..:)
(Shoudn't that have a confirmation window, are you sure you want to ...?)