From the NY1 website:
Major Service Disruptions To Hit F, G Trains This Weekend
February 29, 2008
Riders of the F and G trains in Brooklyn are in for rough time this coming weekend. MTA has announced that there will be no F train service between the Jay Street and 4th Avenue/9th Street stops to allow for signal and track work. The MTA is advising that customers switch to the D train at 4th Avenue/9th Street for service to and from Manhattan.
As for G train riders, there'll be no service between the Hoyt-Schermerhorn and Smith-Ninth Street stops for service to and from Manhattan. As an alternative, there will be free shuttle buses operating between Hoyt-Schermerhorn and 7th Avenue in Brooklyn. The changes will be in effect from midnight Friday through 5 a.m. Monday.
More on weekend service changes from the MTA website: