I usually complain when some site uses RC4 and I can't access it, but unlike the OP I don't do that via twitter (one reason is that I don't even have an account there).
I've sent 2 emails regarding the use of ONLY RC4 on payment sites in my country, and although such emails aren't always acknowledged they did get fixed after I CC-ed their PCI auditors [1] :)
[1] which you can find publicly on Visa's site at 'PCI DSS validated Member Agent Weblisting' http://www.visaeurope.com/receiving-payments/security/downlo...