Twitter's working fine for me. This attack is affecting different people differently; as a DDOS, attacking a distributed system (DNS) with a lot of redundancy, it's possible for some people to be affected badly while others not affected at all.

I briefly lost access to GitHub, but Twitter has been working fine every time I've checked. Posting status messages in multiple venues helps to ensure that even if one channel is down, people might be able to get status from another channel.