Are foreign personal names usually written in katakana, or is this dependent on the type or writing, and the target audience? For example, this Japanese Wikipedia entry on Steven Bradbury uses katakana, while this Wikipedia entry on JRuby uses romaji for the contributors.
As you guessed, it depends on the type of writing and the target audience, and also on the style. In text written for general public, such as newspaper articles, foreign personal names are usually written in katakana. In academic books and papers, it is more common to see names in the Latin script (at least in mathematics and computer science).
As for Wikipedia, a guideline of the Japanese Wikipedia states that foreign names other than Korean and Chinese names should be usually written in katakana. I do not know how strongly this guideline is enforced.