As people from Frankfurt are reading this as well, let me mention a quite specific commuting pattern of which I know it exists, though I don't have an clear idea of its extent:
Several Lufthansa staff, especially pilots and stewardesses, are regularly commuting from the northern Hamburg periphery to Frankfurt, as Lufthansa provides air transport to and from the home location free of charge. According to the latest available commuting statistics (June 2012), some 5,500 persons commute from Hamburg, and 4,300 from Schleswig-Holstein to Hesse (5,000 / 1,900 in the opposite direction). An earlier analysis (2005) for Hesse showed approximately 40% of the commuters from Hamburg and Schleswig-Holstein working in Frankfurt. Lufthansa staff may account for up to half of them (around 2,000). The remainder is probably mostly from the financial sector, spending the week in Frankfurt and the weekend with the family in Hamburg / Holstein, as a friend of mine did for a few years, before getting a CFO position in Hamburg.
Another interesting commuting relation is Berlin->Hamburg (7,700; 4,000 in the opposite direction, both growing by some 4-5% p.a.). High-speed trains connect both cities in 100 minutes. Most of the people I know stay with a friend in Hamburg over the week (to the extent they work in Hamburg at all, and are not on mission elsewhere, e.g. as researcher with the Hamburg Institute for Tropical Diseases). A colleague of mine, working on a part-time contract (3 days a week) resides in Hannover, two more in Gottingen. Hamburg-Bremen commutes are anyway common (4,000 / 2,100).
Commuting between Schleswig-Holstein and Lower Saxony is also quite intense (10,500 /15,100). Most of that should take place on the relation Geesthacht/Lauenburg <-> Lüneburg/Winsen (you may have noted that several communities across the Elbe from Geesthacht, on or close to the Geesthacht-Lüneburg highway, have been picked up by the SPD).
This is almost as bad as America.
