In hindsight, with David S. Goyer (Batman Begins, DaVinci's Demons, and Constantine) as one of the principle writers, and solid production values, it would seem that ABC would have pumped alot into promoting.
I could have missed it due to watching mostly cable programming.
Found the following from the FFWiki ....
note: this doesn't say how well ABC promoted, but does describe how ....
In May 2009 ABC announced its fall lineup, including a 13-episode order of FlashForward.
ABC began an online marketing campaign for the upcoming series with five-second flashes shown on television during the airing of an episode of Lost, and followed by the simple question "What did you see?" Viewers who then searched this phrase online would find the website of the Mosaic Collective, a fictional organization that is dedicated to collecting records of what everyone experienced during the Global Blackout occurring in the pilot episode.
ABC hopes that FlashForward will serve as somewhat of a companion series during Lost 's sixth and final season, and that it will be Lost's replacement after that show's ending in 2010. Lost shares many themes with FlashForward.
FlashForward was originally developed for the pay-cable station HBO, but HBO felt that it would be better fit for a broadcast network. ABC and FOX originally both wanted the project, due to creator Brannon Braga's involvement with the FOX series 24. As FlashForward eventually ended up on ABC, Braga removed himself from the day-to-day work on the series, in order to lessen tensions between the two networks, but remains executive producer.