> Some users surely could use this tip, and you could 
> possibly add it to the FAQ (unter 'Using 
> user:password@address is not working!' and/or 'Can I use 
> username/password authentication on a site?'):

I have added this remark:

Note: If your username and/or password contains a '@' 
character, you may have to replace all '@' occurences by '%
40' so that it can work, such as in user%
40domain.com:foobar@www.foo.com/auth/. You may have to do 
the same for all "special" characters like spaces (%20), 
quotes (%22).. 

Thanks for the hint!