I actually wanted to bring this up a while back too, but it could cause some big issues (forcing SSL in general that is). I wouldn't force all of HN over SSL, but I would make it a lot clearer to users when logging in, if they are logging in over SSL or not (maybe a large text saying click here to log in over SSL? Even though it might look a bit crappy). Or creating filters for IP's that force SSL for certain countries.
Iran for instance blocked all SSL sites a while back, not sure if this is still the case however..