Twitter is as much an information system as it is a communication system. Many magazines or blogs use it to distribute links or news (one-to-many communication) and it is an honor for the content providers to get linked by those popular magazines as many people will get adverted to the (more or less valuable) content. But lately it seems to me that 5 minutes after an interesting link has been published, the website of the content provider is down. So if one magazine with a few thousand followers distributes a link which will get retweeted or rephrased by other magazines or distributors (users with a few hundred or thousand followers), what happens to the content provider?
By the definition of Wikipedia, this is a DDoS Attack:
A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make a computer resource unavailable to its intended users. Although the means to carry out, motives for, and targets of a DoS attack may vary, it generally consists of the concerted efforts of a person or people to prevent an Internet site or service from functioning efficiently or at all, temporarily or indefinitely.
The distribution of the links is surely not intentional by the twitter-users but surely shows some impact on how fast a system can get down by too many requests. In my opinion is in the responsibility of the distributors to set some time before retweeting or republishing a link to extend the time and traffic load between the requests.