Quote Originally Posted by Layne
When you say "jump on the band wagon" it means to do something that everyone else is doing. Literally it means a wagon or vehicle that musicians travel in.
Yep. A similar term is "fair-weather fan." I just thought I'd reply with an example to help any interested parties out:
"American Idol's" increasing popularity is due to the "bandwagon" effect: people at offices around the country discuss the show at work, and naturally their peers feel obliged to "join the bandwagon" so they can fit in.