Sources: n-tv.de and Germany public holidays. In 2008, the date of the May Day and that of the Ascension public holidays will fall on the same date; Thursday, May 1st, a conjunction that has not happened since 1913, and will not happen again until 2160.
Various European countries have reacted differently to this occurrence; Belgium declared the next day, May 2nd, as a one-off public holiday (our post of April 24), while Luxembourg will not declare a day in lieu public holiday (our post of May 15).
Recent media reports would seem to indicate that Germany will not declare a day in lieu public holiday either (although, as usual, it will be difficult to do any business in Germany on the Friday after Ascension).