... and I solved it myself. When I read my own post, I realised it was more likely the issue was with the computer I tried to log into. I had forgotten that a while back, I had created rules in the debian firewall so that only certain machines could log in through ssh. So the problem is solved now, and had nothing to do with mac os x at all. Sorry about this!
I've got a problem with my new mbp, mac os x snow leopard. It can't ssh. I've got no firewall running, can do ssh localhost and can ssh *into* my mbp from another machine, but I can't ssh from the mbp to another computer. If i do
ssh -v 192.168.0.6
which is my wifes debian comp, I get
OpenSSH_5.2p1, OpenSSL 0.9.8k 25 Mar 2009
debug1: Reading configuration data /etc/ssh_config
debug1: Connecting to 192.168.0.6 [192.168.0.6] port 22.
debug1: connect to address 192.168.0.6 port 22: Operation timed out
ssh: connect to host 192.168.0.6 port 22: Operation timed out
I've tried uncommenting "Host *" and "ForwardAgent yes" in /etc/ssh_config (I read you had to do that on some other forum), but it doesn't help. I can ssh into my wife's computer using any other os than mac os x.
This is extremely annoying, since I can't comfortably fetch my old files to this new computer.