According Martin Freeman's offcial website runed by his brother Jamie, Martin is very happy with the reharsals. Listen to what Jamie says : "Work has started on rehearsals for the movie. Martin is rehearsing his role as Arthur Dent in London along with other cast members. It's actually happening, people! :-) Martin has told me he's really enjoying the rehearsals, heaping praise upon his fellow cast members".
In the meantime, MJ Simpson on his own site, tell us that "Kirkpatrick was in fact at Elstree Studios this week and flew back to the USA only yesterday. “The film was in fantastic shape when I last left it on Wednesday evening,” he told me, “with the cast sinking into their roles really nicely. I saw Vogons practising their marching in formation. Awesome. I think people are going to be very happy.”
So if the main actor and the script writer are happy with what is going on we can guess everything's fine. ;)