Due to track maintenance works there S-Bahns S8 and S9 won't be able to access Frankfurt airport from July 9th - 29th. There will be replacement shuttle busses between Airport and Hauptbahnhof from 4am to 1.30am running every 30mins (only).
Andreas, thanks for the heads-up.
Note that the S-bahn will still run from Rüsselsheim to Mainz and Wiesbaden and from Frankfurt Stadion and Niederrad to the Hbf.
There will also be a connecting S-bahn shuttle every half hour from Rüsselsheim to Niederrad (not Stadion) through the Fernbahnhof as well as a shuttle bus between Rüsselsheim and the airport busbahnhof.
The changes are described in a brochure at http://bauarbeiten.bahn.de/docs/2007/hessen/infos/471_645_680_0907-290707.pdf (pg 3 is in English). The brochure has a map of the alternative routes and schedules.
I hope this means they are going to fix the mess in the regional bahnhof. Right now S-bahns and regional trains leave for Frankfurt Hbf (Hoch or Tief) on adjacent tracks (1 and 2). These tracks are served by separate platforms. How nice it would be if they were served by the same platform, so someone could just stand on one platform and catch the next train to the Hbf, regardless of which track