@danja pointed out that there were RDF validation errors in SemanticTweet. Turns out that I hadn’t checked it closely enough before releasing. They key problem was that I was generating a single <foaf:knows> node, with multiple children, rather than one each.
A secondary problem is that some Twitter users don’t provide valid URIs in their [...]

I’ve just released the first pre-alpha (if there is such a thing) version of the semantictweet service.
Basically, it generates a FOAF RDF document for you from your list of Twitter friends and followers. It does this using the Twitter REST API. This service uses public Twitter data only, and so doesn’t need your Twitter username [...]