[jamesbritt]

Well, not quite ...

    Request-URI Too Large

    The requested URL's length exceeds the capacity limit for     
    this server.

Maybe 50+ paragraphs of lorem ipsum was a bit too much.

EDIT: 100K chars didn't quite make it, but ~1K seems ok

[enathu]

Actually you can make several t.co links and merge it together to post it on a tweet. Actually the tweet that this thread linked to have 5 links itself. Simply merging many t.co links with text can make the longest tweet and it works! And 50+ paragraphs is too much for a single URI anyway.

EDIT: Seems now Twitter has fixed the bug and only shows the t.co link not the text or exact URL in the tweet! No more longest tweets! Only t.co links.